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  • 1. Fardos, Akbar
    et al.
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Jamal, Farrukh
    Ali, Hurria
    Noreen, Khadija
    Ahmed, Rashid
    Algorithm to generate efficient circular designs robust to neighbor effects2024Ingår i: Kuwait Journal of Science, ISSN 2307-4108, Vol. 51, nr 1, artikel-id 100135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Minimal circular balanced and strongly balanced neighbor designs (MCBNDs & MCSBNDs) are popular to control neighbor effects and to estimate neighbor and direct effects independently. In this article, an R-coded algorithm is presented to obtain efficient MCBNDs and MCSBNDs for odd v (number of treatments), and its four generalized classes for v even. Developed algorithm has made the construction of the efficient circular designs robust to neighbor effects so easy in blocks of equal and unequal sizes.

  • 2. Riaz, Muhammad
    et al.
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Tahir, M. H.
    Rasheed, H. M. Kashif
    Khan, Abid
    Ahmed, Rashid
    Construction of efficient classes of circular balanced repeated measurements designs with R2024Ingår i: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415XArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    Pharmacology, medicine, psychology, and the animal sciences all employ repeated measurement designs (RMDs). However, RMDs may experience carryover effects, which are the primary cause of bias in treatment effect estimation. In order to eliminate the carryover effects for odd v (the number of treatments), minimal circular balanced and strongly balanced repeated measurement designs (RMDs) are the ones that should be used. The minimal circular partially balanced and weakly balanced RMDs are used for even v. In order to obtain these important classes of minimal circular RMDs in periods of equal, two, and three different sizes, an R-based algorithm is developed in this article. The newly developed algorithm has made so simple the construction of balanced RMDs and their generalized classes. As a result, it is a novel piece of research.

  • 3.
    Oelrich, Oscar
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Villani, Mattias
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ankargren, Sebastian
    Local prediction pools2024Ingår i: Journal of Forecasting, ISSN 0277-6693, E-ISSN 1099-131X, s. 103-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose local prediction pools as a method for combining the predictive distributions of a set of experts conditional on a set of variables believed to be related to the predictive accuracy of the experts. This is done in a two-step process where we first estimate the conditional predictive accuracy of each expert given a vector of covariates-or pooling variables-and then combine the predictive distributions of the experts conditional on this local predictive accuracy. To estimate the local predictive accuracy of each expert, we introduce the simple, fast, and interpretable caliper method. Expert pooling weights from the local prediction pool approaches the equal weight solution whenever there is little data on local predictive performance, making the pools robust and adaptive. We also propose a local version of the widely used optimal prediction pools. Local prediction pools are shown to outperform the widely used optimal linear pools in a macroeconomic forecasting evaluation and in predicting daily bike usage for a bike rental company.

  • 4. Sallnäs Pysander, Eva-Lotta
    et al.
    Mårtensson, Fredrika
    Waern, Annika
    Litsmark, Anna
    Hedblom, Marcus
    Raustorp, Anders
    Ghilagaber, Gebrenegus
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Zhu, Hui
    Nature and digitalisation challenging the traditional playground2024Ingår i: Urban Forestry & Urban Greening, ISSN 1618-8667, E-ISSN 1610-8167, Vol. 93, s. 1-18, artikel-id 128148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Playing outdoors in nature with peers has been attributed most importance forchildren's healthy development but is increasingly marginalised because of the attractiveness of screen-based play. Careful merging of digital technology into outdoor play environments rich on elements from nature could potentially help bridge digital play with more traditional play activities outdoors. A systematic comparison was made of outdoor play in more or less green settings, with and without digital installations or traditional play equipment. The separate and combined role of digital artefacts, play equipment and natural elements, were investigated, with particular focus on the effects of merging digital materials into nature. A group of children aged 6-8 were involved in a field study in a three-week period playing in a traditional playground, a forest and in a forest with digitally enhanced play artefacts. Children's play behaviour was evaluated using a behavioural tracking method, a questionnaire and a contextual interview with the children, and a physical activity measure, in combination with inventories including maps to document the design, and the ecological and physical status of the settings. The study documents differences in children's play behaviour across the three settings. It differs most between the digital forest setting and the forest setting regarding the play categories imaginative play, physical play and rule play and the digital forest setting stands out when it comes to expressive play and imaginative play. It is discussed how particular attributes in the physical environment influence the overall play flow and the interactive effects of natural material and digital material. Ecologically, the forest and the forest with digitally enhanced artefacts were more diverse than the traditional playground, but the natural material present was important for play in all settings.

  • 5.
    Ghilagaber, Gebrenegus
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Larsson, Rolf
    Adjustment of Anticipatory Covariates in Retrospective Surveys: An Expected Likelihood Approach2023Ingår i: Stats, ISSN 2571-905X, Vol. 6, nr 4, s. 1179-1197Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We address an inference issue where the value of a covariate is measured at the date of the survey but is used to explain behavior that has occurred long before the survey. This causes bias because the value of the covariate does not follow the temporal order of events. We propose an expected likelihood approach to adjust for such bias and illustrate it with data on the effects of educational level achieved by the time of marriage on risks of divorce. For individuals with anticipatory educational level (whose reported educational level was completed after marriage), conditional probabilities of having attained the reported level before marriage are computed. These are then used as weights in the expected likelihood to obtain adjusted estimates of relative risks. For our illustrative data set, the adjusted estimates of relative risks of divorce did not differ significantly from those obtained from anticipatory analysis that ignores the temporal order of events. Our results are slightly different from those in two other studies that analyzed the same data set in a Bayesian framework, though the studies are not fully comparable to each other.

  • 6.
    Koskinen, Johan
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. The Melbourne School of Psychological Sciences, Australia.
    Jones, Pete
    Medeuov, Darkhan
    Antonyuk, Artem
    Puzyreva, Kseniia
    Basov, Nikita
    Analysing networks of networks2023Ingår i: Social Networks, ISSN 0378-8733, E-ISSN 1879-2111, Vol. 74, s. 102-117Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider data with multiple observations or reports on a network in the case when these networks themselves are connected through some form of network ties. We could take the example of a cognitive social structure where there is another type of tie connecting the actors that provide the reports; or the study of interpersonal spillover effects from one cultural domain to another facilitated by the social ties. Another example is when the individual semantic structures are represented as semantic networks of a group of actors and connected through these actors’ social ties to constitute knowledge of a social group. How to jointly represent the two types of networks is not trivial as the layers and not the nodes of the layers of the reported networks are coupled through a network on the reports. We propose to transform the different multiple networks using line graphs, where actors are affiliated with ties represented as nodes, and represent the totality of the different types of ties as a multilevel network. This affords studying the associations between the social network and the reports as well as the alignment of the reports to a criterion graph. We illustrate how the procedure can be applied to studying the social construction of knowledge in local flood management groups. Here we use multilevel exponential random graph models but the representation also lends itself to stochastic actor-oriented models, multilevel blockmodels, and any model capable of handling multilevel networks.

  • 7.
    Gustafsson, Oskar
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Villani, Mattias
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Stockhammar, Pär
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Bayesian optimization of hyperparameters from noisy marginal likelihood estimates2023Ingår i: Journal of applied econometrics (Chichester, England), ISSN 0883-7252, E-ISSN 1099-1255, Vol. 38, nr 4, s. 577-595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Bayesian models often involve a small set of hyperparameters determined by maximizing the marginal likelihood. Bayesian optimization is an iterative method where a Gaussian process posterior of the underlying function is sequentially updated by new function evaluations. We propose a novel Bayesian optimization framework for situations where the user controls the computational effort and therefore the precision of the function evaluations. This is a common in econometrics where the marginal likelihood is often computed by Markov chain Monte Carlo or importance sampling methods. The new acquisition strategy gives the optimizer the option to explore the function with cheap noisy evaluations and therefore find the optimum faster. The method is applied to estimating the prior hyperparameters in two popular models on US macroeconomic time series data: the steady-state Bayesian vector autoregressive (BVAR) and the time-varying parameter BVAR with stochastic volatility.

  • 8. Hassan, Jamshaidul
    et al.
    Noreen, Khadija
    Rasheed, H. M. Kashif
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ahmed, Rashid
    Construction of circular quasi rees neighbor designs which can be converted into minimal circular balanced and strongly balanced neighbor designs2023Ingår i: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 52, nr 16, s. 5587-5605Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The response of a treatment (direct effect) applied on a given unit may be affected by the treatments applied to its neighboring units (neighbor effects). Neighbor designs are considered robust to neighbor effects. Minimal neighbor designs are economical, therefore, these are preferred by the experimenters. Method of cyclic shifts (Rule I) provides the minimal neighbor designs for odd v (number of treatments). Method of cyclic shifts (Rule II) provides the minimal circular Quasi Rees neighbor designs for v even which are considered to be the good alternate to the minimal neighbor designs. In this article, for every case of v even, minimal circular Quasi Rees neighbor designs are constructed in such a way that these designs can also be converted directly into minimal circular balanced and strongly balanced neighbor designs.

  • 9. Khan, Abid
    et al.
    Bashir, Zahid
    Rasheed, H. M. Kashif
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ahmed, Rashid
    Construction of minimal circular nearly strongly balanced repeated measurements designs and their conversion2023Ingår i: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, Vol. 52, nr 12, s. 5749-5758Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Repeated measurements designs (RMDs) are very useful and economical but unfortunately, with the use of RMDs, a major source of bias is arisen, that is the carry over effect. Minimal designs which are strongly and nearly strongly balanced, are preferred to estimate the direct and carry over effects independently. In this article, some new classes of minimal circular nearly strongly balanced RMDs are constructed in periods of two and three different sizes which can be converted directly into minimal circular balanced and minimal strongly balanced which are highly efficient.

  • 10.
    Munezero, Parfait
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Ericsson, Stockholm, Sweden.
    Villani, Mattias
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Linköping University, Linköping, Sweden.
    Kohn, Robert
    Dynamic Mixture of Experts Models for Online Prediction2023Ingår i: Technometrics, ISSN 0040-1706, E-ISSN 1537-2723, Vol. 65, nr 2, s. 257-268Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A mixture of experts models the conditional density of a response variable using a mixture of regression models with covariate-dependent mixture weights. We extend the finite mixture of experts model by allowing the parameters in both the mixture components and the weights to evolve in time by following random walk processes. Inference for time-varying parameters in richly parameterized mixture of experts models is challenging. We propose a sequential Monte Carlo algorithm for online inference based on a tailored proposal distribution built on ideas from linear Bayes methods and the EM algorithm. The method gives a unified treatment for mixtures with time-varying parameters, including the special case of static parameters. We assess the properties of the method on simulated data and on industrial data where the aim is to predict software faults in a continuously upgraded large-scale software project. 

  • 11. Holle, Hannah
    et al.
    Ghilagaber, Gebrenegus
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Drees, Randi
    Evaluation of the normal gastrointestinal tract in cats using dual-phase computed tomography2023Ingår i: Journal of Small Animal Practice, ISSN 0022-4510, E-ISSN 1748-5827, Vol. 64, nr 7, s. 463-476Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objectives: In cats, although ultrasonography remains the preferred modality to evaluate the gastrointestinal tract, computed tomographic (CT) examination of the abdomen is commonly performed. However, a normal description of the gastrointestinal tract is lacking. This study describes the conspicuity and contrast enhancement pattern of the normal gastrointestinal tract in cats using dual-phase CT.

    Materials and Methods: Pre- and dual-phase postcontrast (early scan at 30 seconds and late scan mean at 84 seconds) abdominal CT exams of 39 cats without history, clinical signs or diagnosis of gastrointestinal disease were reviewed. The gastrointestinal tract was examined for conspicuity and enhancement pattern using commercially available viewing software (Osirix, v.6.5.2), and diameters of 16 gastrointestinal segments were recorded and compared with published radiographic and ultrasonographic reference values.

    Results: Of the 624 gastrointestinal segments, 530 (84.9%) were identified on precontrast studies and 545 (87.3%) segments on postcontrast studies. Of the gastrointestinal wall segments, 257 (41.2%) were identified on precontrast studies and 314 (50.3%) on postcontrast studies. Gastrointestinal segment diameters correlated well with published normal values, whereas wall thickness measurements usually were smaller compared with sonographic normal values. Early mucosal surface enhancement was frequently seen in the gastric cardia and fundus and ileocolic junction, and a mainly transmural wall enhancement in other gastrointestinal segments.

    Clinical Significance: Dual-phase CT allows for the identification of gastrointestinal tract segments and walls in cats. Contrast enhancement improves conspicuity and demonstrates wall layering in the cardia, fundus and ileocolic junction.

  • 12. Hussain, Sajid
    et al.
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Rashid, Muhammad Sajid
    Ahmed, Rashid
    Families of Extended Exponentiated Generalized Distributions and Applications of Medical Data Using Burr III Extended Exponentiated Weibull Distribution2023Ingår i: Mathematics, E-ISSN 2227-7390, Vol. 11, nr 14, artikel-id 3090Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, four new families named as Weibull extended exponentiated-X (WEE-X), Lomax extended exponentiated-X (LEE-X), Logistic extended exponentiated-X (LGCEE-X), and Burr III extended exponentiated-X (BIIIEE-X) with their quantile functions are proposed. The expressions for distribution function and density function of BIIIEE-X family are written in terms of linear combinations of the exponentiated densities based to parent model. New models, i.e., Weibul extended exponentiated Weibull (WEEW), Lomax extended exponentiated Weibull (LEEW), Logistic extended exponentiated Weibull (LGCEEW), and Burr III extended exponentiated-Weibull (BIIIEEW) distributions are derived, were plotted for functions of probability density and hazard rate at different levels of parameters. Some mathematical properties of the BIIIEEW model are disclosed. The maximum likelihood method for the BIIIEEW model are described. Numerical applications of the BIIIEEW model to disease of cancer datasets are provided.

  • 13.
    Quiroz, Matias
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. ARC Centre of Excellence for Mathematical and Statistical Frontiers (ACEMS), Australia.
    Nott, David J.
    Kohn, Robert
    Gaussian Variational Approximations for High-dimensional State Space Models2023Ingår i: Bayesian Analysis, ISSN 1936-0975, E-ISSN 1931-6690, Vol. 18, nr 3, s. 989-1016Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider a Gaussian variational approximation of the posterior density in high-dimensional state space models. The number of parameters in the covariance matrix of the variational approximation grows as the square of the number of model parameters, so it is necessary to find simple yet effective parametrisations of the covariance structure when the number of model parame-ters is large. We approximate the joint posterior density of the state vectors by a dynamic factor model, having Markovian time dependence and a factor covariance structure for the states. This gives a reduced description of the dependence struc-ture for the states, as well as a temporal conditional independence structure sim-ilar to that in the true posterior. We illustrate the methodology on two examples. The first is a spatio-temporal model for the spread of the Eurasian collared-dove across North America. Our approach compares favorably to a recently proposed ensemble Kalman filter method for approximate inference in high-dimensional hi-erarchical spatio-temporal models. Our second example is a Wishart-based multi-variate stochastic volatility model for financial returns, which is outside the class of models the ensemble Kalman filter method can handle.

  • 14.
    Koskinen, Johan
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Snijders, Tom A B
    Multilevel longitudinal analysis of social networks2023Ingår i: Journal of the Royal Statistical Society: Series A (Statistics in Society), ISSN 0964-1998, E-ISSN 1467-985X, Vol. 186, nr 3, s. 376-400Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Stochastic actor-oriented models (SAOMs) are a modelling framework for analysing network dynamics using network panel data. This paper extends the SAOM to the analysis of multilevel network panels through a random coefficient model, estimated with a Bayesian approach. The proposed model allows testing theories about network dynamics, social influence, and interdependence of multiple networks. It is illustrated by a study of the dynamic interdependence of friendship networks and minor delinquency. Data were available for 126 classrooms in the first year of secondary school, of which 82 were used, containing relatively few missing data points and having not too much network turnover.

  • 15. Robins, Garry
    et al.
    Lusher, Dean
    Broccatelli, Chiara
    Bright, David
    Gallagher, Colin
    Karkavandi, Maedeh Aboutalebi
    Matous, Petr
    Coutinho, James
    Wang, Peng
    Koskinen, Johan
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Roden, Bopha
    Sadewo, Giovanni Radhitio Putra
    Multilevel network interventions: Goals, actions, and outcomes2023Ingår i: Social Networks, ISSN 0378-8733, E-ISSN 1879-2111, Vol. 72, s. 108-120Artikel i tidskrift (Refereegranskat)
  • 16. Gallagher, Colin
    et al.
    Lusher, Dean
    Koskinen, Johan
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. University of Melbourne, Australia.
    Roden, Bopha
    Wang, Peng
    Gosling, Aaron
    Polyzos, Anastasios
    Stenzel, Martina
    Hegarty, Sarah
    Spurling, Thomas
    Simpson, Gregory
    Network patterns of university-industry collaboration: A case study of the chemical sciences in Australia2023Ingår i: Scientometrics, ISSN 0138-9130, E-ISSN 1588-2861, Vol. 128, nr 8, s. 4559-4588Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    University-industry (U-I) collaboration takes on many forms, from research services, teaching and training, to curiosity-led research. In the chemical industries, academic chemists generate new knowledge, address novel problems faced by industry, and train the future workforce in cutting-edge methods. In this study, we examine the dynamic structures of collaborative research contracts and grants between academic and industry partners over a 5-year period within a research-intensive Australian university. We reconstruct internal contract data provided by a university research office as records of its collaborations into a complex relational database that links researchers to research projects. We then structure this complex relational data as a two-mode network of researcher-project collaborations for utilisation with Social Network Analysis (SNA)-a relational methodology ideally suited to relational data. Specifically, we use a stochastic actor-oriented model (SAOM), a statistical network model for longitudinal two-mode network data. Although the dataset is complicated, we manage to replicate it exactly using a very parsimonious and relatable network model. Results indicate that as academics gain experience, they become more involved in direct research contracts with industry, and in research projects more generally. Further, more senior academics are involved in projects involving both industry partners and other academic partners of any level. While more experienced academics are also less likely to repeat collaborations with the same colleagues, there is a more general tendency in these collaborations, regardless of academic seniority or industry engagement, for prior collaborations to predict future collaborations. We discuss implications for industry and academics.

  • 17. Nadeem, Muhammad
    et al.
    Noreen, Khadija
    Kashif Rasheed, H. M.
    Ahmed, Rashid
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    New generators for minimal circular generalised neighbour designs in blocks of two different sizes2023Ingår i: Statistics in Transition New Series, ISSN 1234-7655, Vol. 24, nr 2, s. 85-92Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Minimal neighbour designs (NDs) are used when a response of a treatment (direct effect) is affected by the treatment(s) applied in the neighbouring units. Minimal generalised NDs are preferred when minimal NDs cannot be constructed. Through the method of cyclic shifts (Rule I), the conditions for the existence of minimal circular generalised NDs are discussed, in which v/2 unordered pairs do not appear as neighbours. Certain generators are also developed to obtain minimal circular generalised NDs in blocks of two different sizes, where k2 = 3, 4 and 5. All these designs are constructed using i sets of shifts for k1 and two for k2. 

  • 18.
    Tsirpitzi, Renata Eirini
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Miller, Frank
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Linköping University, Sweden.
    Burman, Carl-Fredrik
    Robust optimal designs using a model misspecification term2023Ingår i: Metrika (Heidelberg), ISSN 0026-1335, E-ISSN 1435-926X, nr 86, s. 781-804Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Much of classical optimal design theory relies on specifying a model with only a small number of parameters. In many applications, such models will give reasonable approximations. However, they will often be found not to be entirely correct when enough data are at hand. A property of classical optimal design methodology is that the amount of data does not influence the design when a fixed model is used. However, it is reasonable that a low dimensional model is satisfactory only if limited data is available. With more data available, more aspects of the underlying relationship can be assessed. We consider a simple model that is not thought to be fully correct. The model misspecification, that is, the difference between the true mean and the simple model, is explicitly modeled with a stochastic process. This gives a unified approach to handle situations with both limited and rich data. Our objective is to estimate the combined model, which is the sum of the simple model and the assumed misspecification process. In our situation, the low-dimensional model can be viewed as a fixed effect and the misspecification term as a random effect in a mixed-effects model. Our aim is to predict within this model. We describe how we minimize the prediction error using an optimal design. We compute optimal designs for the full model in different cases. The results confirm that the optimal design depends strongly on the sample size. In low-information situations, traditional optimal designs for models with a small number of parameters are sufficient, while the inclusion of the misspecification term lead to very different designs in data-rich cases. 

  • 19.
    Noreen, Khadija
    et al.
    The Islamia University of Bahawalpur, Bahawalpur, Pakistan.
    Tahir, M. H.
    The Islamia University of Bahawalpur, Bahawalpur, Pakistan.
    Rasheed, Muhammad
    The Islamia University of Bahawalpur, Bahawalpur, Pakistan.
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ahmed, Rashid
    The Islamia University of Bahawalpur, Bahawalpur, Pakistan.
    Some important classes of non-directional minimal circular weakly balanced neighbor designs2023Ingår i: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, s. 1-10Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Minimal neighbor designs are useful to balance out neighbor effects economically. The method of cyclic shifts provides the construction of these minimal designs in circular blocks only for v odd, where v is the number of treatments to be compared. Minimal circular weakly balanced neighbor designs are used for v even. In this article, two classes of minimal circular weakly balanced neighbor designs are constructed for v even. In class I, v/2 of all unordered pairs of two distinct treatments appear twice as neighbors while the remaining ones appear once. In class II, 3v/2 of all unordered pairs appear twice as neighbors.

  • 20.
    Jederlund, Ulf
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Specialpedagogiska institutionen.
    von Rosen, Tatjana
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Teacher-student relationships and students' self-efficacy beliefs. Rationale, validation and further potential of two instruments2023Ingår i: Education Inquiry, E-ISSN 2000-4508, Vol. 14, nr 4, s. 529-553Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    High quality of teacher–student relationships is widely recognized as fundamental part of good education. Moreover, students’ self-efficacy beliefs, or their confidence to succeed within different domains at school, are important impact factors to achievement. Although there is support for an association between student-perceived teacher–student relationship quality and students’ self-efficacy judgements, which mediates achievement, no tool explores this association. This article suggests that two instruments, respectively measuring students’ perceptions of teacher–student relationship quality (TSR) and student’s self-efficacy (SSE), can be used in parallel for a multifaceted exploration of individual students’ perception of TSR quality, in relationship to their self-efficacy. Two well-established instruments were adopted, validated and their factor structures re-confirmed in a Swedish sample, using data from students in five schools (n=382). Factor analysis showed that models with three underlying dimensions of TSR and four underlying dimensions of SSE were the most appropriate. All sub-scales showed good-to-excellent reliability (Cronbach’s α = 0.75–0.94). Findings indicated a lack of multigroup invariance across gender and school level for the TSR-model. Substantial associations were found between student-perceived teacher support, and students’ self-efficacy for self-regulated learning and global academic success. We discuss utility and limitations, need of model improvement, and future potential.   

  • 21. Armelius, Hanna
    et al.
    Solberger, Martin
    Spånberg, Erik
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Österholm, Pär
    The evolution of the natural rate of interest: evidence from the Scandinavian countries2023Ingår i: Empirical Economics, ISSN 0377-7332, E-ISSN 1435-8921Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, the natural rate of interest in Denmark, Norway and Sweden is estimated. This is done by augmenting the Laubach and Williams (Rev Econ Stat 85:1063–1070, 2003) framework with a dynamic factor model linked to economic indicators––a modelling choice which allows us to better identify business cycle fluctuations. We estimate the model using Bayesian methods on data ranging from 1990Q1 to 2022Q4. The results indicate that the natural rate has declined substantially and in all countries is at a low level at the end of the sample. 

  • 22. Hussain, Sajid
    et al.
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Sajid Rashid, Muhammad
    Ahmed, Rashid
    The Exponentiated Power Alpha Index Generalized Family of Distributions: Properties and Applications2023Ingår i: Mathematics, E-ISSN 2227-7390, Vol. 11, nr 4, s. 900-900Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The study of hydrological characteristics has a vital role in designing, planning, and managing water resources. The selection of appropriate probability distributions and methods of estimations are basic elements in hydrology analyses. In this article, a new family named the ‘exponentiated power alpha index generalized’ (EPAIG)-G is proposed to develop several new distributions. Using this proposed family, we developed a new model, called the EPAIG-exponential (EPAIG-E). A few structural properties of the EPAIG-G were obtained. The EPAIG-E parameters were estimated through the method of maximum likelihood (MML). The study of the Monte Carlo simulation (MCS) was produced for the EPAIG-E. The model performance is illustrated using real data.

  • 23. Ahmed, Imaduddin
    et al.
    Parikh, Priti
    Munezero, Parfait
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Ericsson, Sweden.
    Sianjase, Graham
    Coffman, D'Maris
    The impact of power outages on households in Zambia2023Ingår i: Economia Politica, ISSN 1120-2890, E-ISSN 1973-820X, nr 40, s. 835-867Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As global average temperatures rise, so does the frequency and intensity of El Niño-induced droughts, which in turn threaten the reliability of hydropower. 1.4 billion people live in countries where hydropower constitutes more than a quarter of the electricity production and which have experienced El Niño droughts, meaning many more power outages can be expected around the world. Little research has been conducted on the impact of power outages on mental health. This study takes Zambia as its case study to examine the impact that El Niño droughts have had on the lives of householders connected to a highly hydropower-dependant electricity grid, and includes the impact it has had on their physical and self-reported mental health. Using 54 online responses to a survey, we found that the greatest impacts of outages spoiled food, compromised entertainment, compromised ability to work and limitation in cooking options. More than a fifth of respondents reported experiencing self-reported depression to a major degree or all of the time due to power outages, with individuals writing their own responses that they felt debilitated, experienced reduced communication and reduced activities, and stress. Using Bayesian inference, we found that changes in sleeping patterns arising from power outages was a statistically significant predictor of self-reported depression. 63% of surveyed households were willing to pay approximately USD 0.10/kWh as of the end of 2019, about double the tariff that they did, to ensure reliable electricity supply. Household income was a statistically significant predictor of willingness to pay more.

  • 24.
    Andersson, Per Gösta
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    The Wald Confidence Interval for a Binomial p as an Illuminating “Bad” Example2023Ingår i: American Statistician, ISSN 0003-1305, E-ISSN 1537-2731, Vol. 77, nr 4, s. 443-448Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    When teaching we usually not only demonstrate/discuss how a certain method works, but, not less important, why it works. In contrast, the Wald confidence interval for a binomial p constitutes an excellent example of a case where we might be interested in why a method does not work. It has been in use for many years and, sadly enough, it is still to be found in many textbooks in mathematical statistics/statistics. The reasons for not using this interval are plentiful and this fact gives us a good opportunity to discuss all of its deficiencies and draw conclusions which are of more general interest. We will mostly use already known results and bring them together in a manner appropriate to the teaching situation. The main purpose of this article is to show how to stimulate students to take a more critical view of simplifications and approximations. We primarily aim for master’s students who previously have been confronted with the Wilson (score) interval, but parts of the presentation may as well be suitable for bachelor’s students. 

  • 25. Rodriguez-Deniz, Hector
    et al.
    Villani, Mattias
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Linköping University, Sweden.
    Voltes-Dorta, Augusto
    A multilayered block network model to forecast large dynamic transportation graphs: An application to US air transport2022Ingår i: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 137, artikel-id 103556Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Dynamic transportation networks have been analyzed for years by means of static graph-based indicators in order to study the temporal evolution of relevant network components, and to reveal complex dependencies that would not be easily detected by a direct inspection of the data. This paper presents a state-of-the-art probabilistic latent network model to forecast multilayer dynamic graphs that are increasingly common in transportation and proposes a community-based extension to reduce the computational burden. Flexible time series analysis is obtained by modeling the probability of edges between vertices through latent Gaussian processes. The models and Bayesian inference are illustrated on a sample of 10-year data from four major airlines within the US air transportation system. Results show how the estimated latent parameters from the models are related to the airlines’ connectivity dynamics, and their ability to project the multilayer graph into the future for out-of-sample full network forecasts, while stochastic blockmodeling allows for the identification of relevant communities. Reliable network predictions would allow policy-makers to better understand the dynamics of the transport system, and help in their planning on e.g. route development, or the deployment of new regulations.

  • 26.
    Lachmann, Jon
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Storvik, Geir
    Frommlet, Florian
    Hubin, Aliaksandr
    A subsampling approach for Bayesian model selection2022Ingår i: International Journal of Approximate Reasoning, ISSN 0888-613X, E-ISSN 1873-4731, Vol. 151, s. 33-63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is common practice to use Laplace approximations to decrease the computational burden when computing the marginal likelihoods in Bayesian versions of generalised linear models (GLM). Marginal likelihoods combined with model priors are then used in different search algorithms to compute the posterior marginal probabilities of models and individual covariates. This allows performing Bayesian model selection and model averaging. For large sample sizes, even the Laplace approximation becomes computationally challenging because the optimisation routine involved needs to evaluate the likelihood on the full dataset in multiple iterations. As a consequence, the algorithm is not scalable for large datasets. To address this problem, we suggest using stochastic optimisation approaches, which only use a subsample of the data for each iteration. We combine stochastic optimisation with Markov chain Monte Carlo (MCMC) based methods for Bayesian model selection and provide some theoretical results on the convergence of the estimates for the resulting time-inhomogeneous MCMC. Finally, we report results from experiments illustrating the performance of the proposed algorithm. 

  • 27. Noreen, Khadija
    et al.
    Rashid, Muhammad Sajid
    Shehzad, Farrukh
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Noreen, Zahra
    Omer, Talha
    Ahmed, Rashid
    Algorithms to obtain generalized neighbor designs in minimal circular blocks2022Ingår i: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, s. 1-12Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The experiments where response of a treatment (direct effect) is affected by the treatment(s) applied in neighboring units, neighbor designs are used to balance the neighbor effects. Being the economical, minimal neighbor designs are preferred by the experimenters. Minimal circular neighbor designs could not be constructed for almost every case of v even, where v is number of treatments. For v even, minimal circular generalized neighbor designs are preferred. In this article, algorithms are developed to obtain minimal circular generalized neighbor designs in which (a) v/2 of the unordered pairs, and (b) 3v/2 of the unordered pairs, do not appear as neighbor whereas the remaining ones appear once. These algorithms are also coded with R-language. 

  • 28.
    Andersson, Per Gösta
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Approximate Confidence Intervals for a Binomial p—Once Again2022Ingår i: Statistical Science, ISSN 0883-4237, E-ISSN 2168-8745, Vol. 37, nr 4, s. 598-606Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of constructing a reasonably simple yet wellbehaved confidence interval for a binomial parameter p is old but still fascinating and surprisingly complex. During the last century, many alternatives to the poorly behaved standard Wald interval have been suggested. It seems though that the Wald interval is still much in use in spite of many efforts over the years through publications to point out its deficiencies. This paper constitutes yet another attempt to provide an alternative and it builds on a special case of a general technique for adjusted intervals primarily based on Wald type statistics. The main idea is to construct an approximate pivot with uncorrelated, or nearly uncorrelated, components. The resulting AN (Andersson–Nerman) interval, as well as a modification thereof, is compared with the well-renowned Wilson and AC (Agresti–Coull) intervals and the subsequent discussion will in itself hopefully shed some new light on this seemingly elementary interval estimation situation. Generally, an alternative to the Wald interval is to be judged not only by performance, its expression should also indicate why we will obtain a better behaved interval. It is argued that the well-behaved AN interval meets this requirement.

  • 29. Söderström, Lisa
    et al.
    Forslund, Marina
    Johansson, Birgitta
    Ottenblad, Anna
    Rosenblad, Andreas
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Uppsala University, Sweden; Regional Cancer Centre Stockholm-Gotland, Sweden.
    Associations between dietary advice on modified fibre and lactose intakes and nutrient intakes in men with prostate cancer undergoing radiotherapy2022Ingår i: Upsala Journal of Medical Sciences, ISSN 0300-9734, E-ISSN 2000-1967, Vol. 127, nr 1, artikel-id e8261Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objectives: A variety of non-evidence-based dietary advice on modified fibre and lactose intakes are provided to patients undergoing pelvic radiotherapy to counteract treatment-related bowel symptoms. More knowledge on the nutritional consequences of such advice is needed. This study aimed to explore how advice on modified fibre and lactose intakes during pelvic radiotherapy was associated with nutrient intakes amongst patients with prostate cancer.

    Methods: A total of 77 Swedish men who underwent radiotherapy (50/2 Gy + boost 20–30 Gy) in 2009–2014 due to prostate cancer were given dietary advice at radiotherapy onset (baseline) and at 4 and 8 weeks after radiotherapy onset, to modify their fibre and lactose intakes. At baseline, the participants completed a food frequency questionnaire (FFQ) and a 24-h dietary recall. At 4 and 8 weeks, the participants completed the FFQ and a 4-day estimated food record.

    Fibre and lactose intakes were measured by intake scores calculated from the FFQs. Multiple linear regression models were used to analyse associations between intake scores and fibre- and lactose-related nutrients.

    Results: In adjusted analyses, there were few significant associations between dietary advice on modified fibre and lactose intakes and observed intakes of fibre- and lactose-related nutrients. A more modified lactose intake was thus associated with a lower intake of calcium (P = 0.041), whilst a more modified fibre intake was associated with a higher value for the change in intake of vitamin C (P = 0.016).

    Conclusions: Dietary advice on modified fibre and lactose intake was in most cases not significantly associated with altered nutrient intakes, rather the energy and nutrient intakes were mostly stable during the pelvic radiotherapy. More research is needed on the nutritional consequences of dietary advice on modified fibre and lactose intakes to reach consensus on if they should continue to be provided in the clinic.

  • 30.
    Jederlund, Ulf
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Specialpedagogiska institutionen.
    von Rosen, Tatjana
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Changes in Students’ School Trust as a Reflection of Teachers’ Collective Learning Processes: Findings from a Longitudinal Study2022Ingår i: Scandinavian Journal of Educational Research, ISSN 0031-3831, E-ISSN 1470-1170, Vol. 66, nr 7, s. 1161-1182Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This 2-year longitudinal study compares students’ trajectories for perceived teacher–student relationship quality and students’ selfefficacy (together discussed as students’ school trust) to previously documented teacher-perceived experiences in teacher teams’ collective learning processes. The article’s main contribution is the reflection in students’ perceptions, of their teachers’ perceived quality and attainment in collective learning processes. Comparisons between schools show that trajectories for students belonging to the only teacher team that experienced a more mature and successful learning process in an earlier study, differed significantly from the trajectories for students in compared teams. Differences demonstrated large positive effect sizes (d=0.81–1.14). Individual analysis provides deeper insights about how these students’ perceptions changed. Additionally, the full sample data confirms earlier findings of substantial cross-associations between student-perceived teacher–student relationship quality and student self-efficacy. For example, sustainable associations between supportive teacher–student relationships and students’ global academic self-efficacy and self-efficacy for self-regulative learning were found (r = 0.43–0.51).

  • 31.
    Ghilagaber, Gebrenegus
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Uppsala University, Uppsala, Sweden.
    Developing an Empirical Demographic Typology of African Countries at the Turn of the Century: The Use of Principal Components-, Cluster- and Discriminant Analyses2022Ingår i: Eritrean Studies Journal, Vol. 1, nr 1, s. 49-79Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using a combination of multivariate techniques, this paper attemptsto build a classification for 53 African countries with respect to their demographic profiles. Principal Components Analys is applied on 13 demographic indicators allowed for a choice of 3 Principal Components which accounted for 84% of the total variation in the original indicators. The first principal component that accounted for 53% of the variation in the original variables is acontrast between fertility, mortality, and proportion of young peopleon the one hand, and life expectancy and proportion of older people on the other. The second component, accounting for 23%of the variation, is reflection of the actual (1998) and forecasted (2025 and 2050) population sizes. The third component, accounting for 8% of the variation, is basically the population density.

    Cluster Analysis was then applied on these three Principal Components with a view of constructing a classification of the countries. The empirical results reveal that the countries in Northern Africa make their own cluster and that only two countries from the other part of Africa fall in this cluster of North African countries. Further, the three most populated countries of Sub-Saharan Africa make their own cluster. Else, the results show no unique spatial mix of the other countries. A separate discriminant analysis, on the other hand, classifies the seven North African countriesin one cluster (100 % correct classification). Among the 16 countries in West Africa 69 % were classified correctly while the corresponding figures of correct classification for East, Central and Southern Africa were 65 %, 63 % and 60 %, respectively. Thus, the results support a classification of Africa into North Africa and the rest (Sub-Saharan Africa) with respect to demographic profiles. However, any attempt to classify countries in the rest (Sub-Saharan) Africa with respect to their demographicbe havior should be based on other (such as socioeconomic, political, etc.) indicators rather than on spatial classification. A deeper investigation on similarities of the countries that fall in respective clusters and a follow-up of the study with more recent data could be areas worth investigating in the future.

  • 32.
    ul Hassan, Mahmood
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Miller, Frank
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Discrimination with unidimensional and multidimensional item response theory models for educational data2022Ingår i: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, Vol. 51, nr 6, s. 2992-3012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Achievement tests are used to characterize the proficiency of higher-education students. Item response theory (IRT) models are applied to these tests to estimate the ability of students (as latent variable in the model). In order for quality IRT parameters to be estimated, especially ability parameters, it is important that the appropriate number of dimensions is identified. Through a case study, based on a statistics exam for students in higher education, we show how dimensions and other model parameters can be chosen in a real situation. Our model choice is based both on empirical and on background knowledge of the test. We show that dimensionality influences the estimates of the item-parameters, especially the discrimination parameter which provides information about the quality of the item. We perform a simulation study to generalize our conclusions. Both the simulation study and the case study show that multidimensional models have the advantage to better discriminate between examinees. We conclude from the simulation study that it is safer to use a multidimensional model compared to a unidimensional if it is unknown which model is the correct one.

  • 33.
    Munezero, Parfait
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ghilagaber, Gebrenegus
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Dynamic Bayesian adjustment of anticipatory covariates in retrospective data: application to the effect of education on divorce risk2022Ingår i: Journal of Applied Statistics, ISSN 0266-4763, E-ISSN 1360-0532, Vol. 49, nr 6, s. 1382-1401Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We address a problem in inference from retrospective studies where the value of a variable is measured at the date of the survey but is used as covariate to events that have occurred long before the survey. This causes problem because the value of the current-date (anticipatory) covariate does not follow the temporal order of events. We propose a dynamic Bayesian approach for modelling jointly the anticipatory covariate and the event of interest, and allowing the effects of the anticipatory covariate to vary over time. The issues are illustrated with data on the effects of education attained by the survey-time on divorce risks among Swedish men. The overall results show that failure to adjust for the anticipatory nature of education leads to elevated relative risks of divorce across educational levels. The results are partially in accordance with previous findings based on analyses of the same data set. More importantly, our findings provide new insights in that the bias due to anticipatory covariates varies over marriage duration.

  • 34.
    ul Hassan, Mahmood
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Jabeen, Rida
    Ahmed, Rashid
    Sajjad, Muhammad
    Efficient Minimal Circular Strongly Partially Balanced RMDs in Periods of Two Different Sizes2022Ingår i: Thailand statistician, ISSN 1685-9057, Vol. 20, nr 1, s. 80-97Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Balanced or strongly balanced repeated measurements designs (RMDs) are used to balance out residual effects Minimal strongly balanced RMD (SBRMDs) are important to estimate the direct effects and residual effects independently at low cost but there are many situations where SBRMDs cannot be constructed. In such situations, strongly partially balanced RMDs (SPBRMDs) are preferred. In literature, these designs are not available for odd p(1) (larger period size). In this paper, minimal circular SPBRMDs are constructed in periods of two different sizes for almost every case of p(1) (odd).

  • 35. Jabeen, Rida
    et al.
    Khan, Abid
    Rasheed, H. M. Kashif
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ahmed, Rashid
    General construction of efficient circular partially strongly-balanced repeated measurements designs2022Ingår i: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, s. 1-11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Residual effects in repeated measurements design (RMDs) leads to wrong estimation of direct treatment effects. Minimal strongly balanced RMDs are preferred to balance out the residual effects. The partially strongly balanced designs form an important family of RMDs which provide designs where minimal strongly balanced RMDs do not exist. In this article, a general construction of efficieint circular partially strongly-balanced RMDs is given in periods of k different sizes which produces these designs in periods of equal sizes, two different sizes, three different sizes, …, by putting k = 1, 2, 3, …, respectively. 

  • 36. Liang, Yuli
    et al.
    Coelho, Carlos A.
    von Rosen, Tatjana
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Hypothesis testing in multivariate normal models with block circular covariance structures2022Ingår i: Biometrical Journal, ISSN 0323-3847, E-ISSN 1521-4036, Vol. 64, nr 3, s. 557-576Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this article, we address the problem of simultaneous testing hypothesis about mean and covariance matrix for repeated measures data when both the mean vector and covariance matrix are patterned. In particular, tests about the mean vector under block circular and doubly exchangeable covariance structures have been considered. The null distributions are established for the corresponding likelihood ratio test statistics, and expressions for the exact or near-exact probability density and cumulative distribution functions are obtained. The application of the results is illustrated by both a simulation study and a real-life data example.

  • 37.
    Högnäs, Robin S.
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Psykologiska institutionen, Stressforskningsinstitutet.
    Bijlsma, Maarten J.
    Högnäs, Ulf
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Blomqvist, Sandra
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Psykologiska institutionen, Stressforskningsinstitutet.
    Westerlund, Hugo
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Psykologiska institutionen, Stressforskningsinstitutet.
    Magnusson Hanson, Linda
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Psykologiska institutionen, Stressforskningsinstitutet.
    It's giving me the blues: A fixed-effects and g-formula approach to understanding job insecurity, sleep disturbances, and major depression2022Ingår i: Social Science and Medicine, ISSN 0277-9536, E-ISSN 1873-5347, Vol. 297, artikel-id 114805Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Research suggests that work-related factors like job insecurity increases the risk of major depression (MD), although it is unclear whether the association is causal. Research further suggests that job insecurity increases sleep disturbances, which is also a risk factor for MD. Based on current knowledge, it is possible that job insecurity operates through sleep disturbances to affect MD, but this pathway has not been examined in the literature. The current study extends the literature by using two complementary, counterfactual approaches (i.e., random- and fixed-effects regression and a mediational g-formula) to examine whether job insecurity causes MD and whether sleep disturbances mediate the relationship. A methodological triangulation approach allowed us to adjust for unobserved and intermediate confounding, which has not been addressed in prior research. Findings suggest that the relationship between job insecurity and MD is primarily direct, that hypothetically intervening on job insecurity (in our g-formula) would reduce MD by approximately 10% at the population level, and this relationship operates via sleep disturbances to some degree. However, the indirect pathway had a high degree of uncertainty.

  • 38. Agneessens, Filip
    et al.
    Trincado-Munoz, Francisco J.
    Koskinen, Johan
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Network formation in organizational settings: Exploring the importance of local social processes and team-level contextual variables in small groups using bayesian hierarchical ERGMs2022Ingår i: Social Networks, ISSN 0378-8733, E-ISSN 1879-2111Artikel i tidskrift (Refereegranskat)
  • 39. Li, Yiming
    et al.
    Alharthi, Majed
    Ahmad, Ishtiaq
    Hanif, Imran
    Ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Nexus between renewable energy, natural resources and carbon emissions under the shadow of transboundary trade relationship from South East Asian economies2022Ingår i: Energy Strategy Reviews, ISSN 2211-467X, E-ISSN 2211-4688, Vol. 41, artikel-id 100855Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This study determined the influence of renewable energy and natural resources on carbon emissions by paying special attention to the transboundary trade relationship between South East Asian (SEA) economies. To highlight the importance of international trade relationships among the SEA economies, an interaction term is introduced. Moreover, to estimate the results, panel data from 1996 to 2019 is analyzed by applying Cross-Sectional Augmented Autoregressive Distributed Lag (CS-ARDL). The results show that renewable energy consumption is a significant factor that can reduce carbon emissions. The employment of interaction term shows that international trade improves the influence of renewable energy to control carbon emissions. The findings also depict that natural resources consumption is stimulating carbon emissions. While a strong trade bond is helping to reduce the influence of natural resources consumption on carbon emissions. The findings of this study highlight the importance of international trade at the regional level to mitigate carbon emissions. The study suggests that improvement in international trade may prove a helpful strategy to promote renewable energy sources and diminish the reliance on natural resources such as fossil fuels, this will ultimately help to mitigate carbon emissions.

  • 40. Omer, Talha
    et al.
    Ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Hussain, Ijaz
    Ilyas, Maryam
    Din Hashmi, Syed Ghulam Mohayud
    Khan, Yousaf Ali
    Optimization of Monitoring Network to the Rainfall Distribution by Using Stochastic Search Algorithms: Lesson from Pakistan2022Ingår i: Tellus. Series A, Dynamic meteorology and oceanography, ISSN 0280-6495, E-ISSN 1600-0870, Vol. 74, nr 1, s. 333-345Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Agricultural production is greatly influenced by environmental parameters such as temperature, rainfall, humidity, and wind speed. The accurate information about environmental parameters plays a vital and useful role when making policies for the agriculture sector as well as for other sectors. Pakistan meteorological department observed these environmental parameters at more than 90 stations. The allocation of these monitoring stations is not made systematically correct. This leads to inaccurate predictions for unobserved locations. The study aims to propose a monitoring network by which these prediction errors of the environmental parameters can be minimized. The well-known prediction techniques named, model-based ordinary kriging and model-based universal kriging (UK) with the known Matheron variogram model are used for prediction purposes. We investigate the monitoring network of Pakistan for rainfall and focus on both the optimal deletion/addition of monitoring stations from/to this network. The two stochastic search algorithms, spatial simulated annealing, and genetic algorithm are used for optimization purposes. Furthermore, the minimization of the Average Kriging Variance (AKV) is taken as the interpolation accuracy measure. The spatial simulated annealing exhibits a lower AKV as compared to the Genetic algorithm when adding/removing the optimal/redundant locations from the monitoring network.

  • 41. Rodriguez-Deniz, Hector
    et al.
    Villani, Mattias
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Linköping University, Sweden.
    Robust Real-Time Delay Predictions in a Network of High-Frequency Urban Buses2022Ingår i: IEEE transactions on intelligent transportation systems (Print), ISSN 1524-9050, E-ISSN 1558-0016, Vol. 23, nr 9, s. 16304-16317Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Providing transport users and operators with accurate forecasts on travel times is challenging due to a highly stochastic traffic environment. Public transport users are particularly sensitive to unexpected waiting times, which negatively affect their perception on the system's reliability. In this paper we develop a robust model for real-time bus travel time prediction that departs from Gaussian assumptions by using Student-t errors. The proposed approach uses spatiotemporal characteristics from the route and previous bus trips to model short-term effects, and date/time variables and Gaussian processes for long-run forecasts. The model allows for flexible modeling of mean, variance and kurtosis spaces. We propose algorithms for Bayesian inference and for computing probabilistic forecast distributions. Experiments are performed using data from high-frequency buses in Stockholm, Sweden. Results show that Student-t models outperform Gaussian ones in terms of log-posterior predictive power to forecast bus delays at specific stops, which reveals the importance of accounting for predictive uncertainty in model selection. Estimated Student-t regressions capture typical temporal variability between within-day hours and different weekdays. Strong spatiotemporal effects are detected for incoming buses from immediately previous stops, which is in line with many recently developed models. We finally show how Bayesian inference naturally allows for predictive uncertainty quantification, e.g. by returning the predictive probability that the delay of an incoming bus exceeds a given threshold.

  • 42. van den Hurk, Wobbie
    et al.
    Bergman, Ingvar
    Machado, Alejandra
    Bjermo, Jonas
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Gustavsson, Anders
    Swedish Normative Data for Mindmore: A Comprehensive Cognitive Screening Battery, Both Digital and Self-Administrated2022Ingår i: Journal of the International Neuropsychological Society, ISSN 1355-6177, E-ISSN 1469-7661, Vol. 28, nr 2, s. 188-202, artikel-id PII S135561772100045XArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    Objective: Cognitive impairment is a key element in most mental disorders. Its objective assessment at initial patient contact in primary care can lead to better adjusted and timely care with personalised treatment and recovery. To enable this, we designed the Mindmore self-administrative cognitive screening battery. What is presented here is normative data for the Mindmore battery for the Swedish population. Method: A total of 720 healthy adults (17 to 93 years) completed the Mindmore screening battery, which consists of 14 individual tests across five cognitive domains: attention and processing speed, memory, language, visuospatial functions and executive functions. Regression-based normative data were established for 42 test result measures, investigating linear, non-linear and interaction effects between age, education and sex. Results: The test results were most affected by age and to a lesser extent by education and sex. All but one test displayed either linear or accelerated age-related decline, or a U-shaped association with age. All but two tests showed beneficial effects of education, either linear or subsiding after 12 years of educational attainment. Sex affected tests in the memory and executive domains. In three tests, an interaction between age and education revealed an increased benefit of education later in life. Conclusion: This study provides normative models for 14 traditional cognitive tests adapted for self-administration through a digital platform. The models will enable more accurate interpretation of test results, hopefully leading to improved clinical decision making and better care for patients with cognitive impairment.

  • 43. Hussain, Sajid
    et al.
    Rashid, Muhammad Sajid
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ahmed, Rashid
    The Generalized Alpha Exponent Power Family of Distributions: Properties and Applications2022Ingår i: Mathematics, E-ISSN 2227-7390, Vol. 10, nr 9, artikel-id 1421Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here, a new method is recommended to characterize a new continuous distribution class, named the generalized alpha exponent power family of distributions (GAEPFDs). A particular sub-model is presented for exemplifying the objective. The basic statistical properties, such as ordinary moments, the probability weighted moments, mode, quantile, order statistics, entropy measures, and moment generating functions, etc., were explored. To gauge the GAEPPRD parameters, the ML technique was utilized. The estimator behaviour was studied by a Monte Carlo simulation study (MCSS). The effectiveness of GAEPFDs was demonstrated observationally through lifetime data. The applications show that GAEPFDs can offer preferable results over other competitive models.

  • 44. Hussain, Sajid
    et al.
    Sajid Rashid, Muhammad
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ahmed, Rashid
    The Generalized Exponential Extended Exponentiated Family of Distributions: Theory, Properties, and Applications2022Ingår i: Mathematics, E-ISSN 2227-7390, Vol. 10, nr 19, artikel-id 3419Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Here, we propose a new generalized exponential extended exponentiated (NGE3) family of distributions. Some statistical properties of proposed family are gained. The most extreme probability method, maximum likelihood (ML), is utilized for parameter estimation. We explore an exceptional model called NGE3-Exponential (NGE3E). NGE3E is estimated with ML, and the performance of estimators is demonstrated by utilizing a simulation. Moreover, two applications are given to show the significance and adaptability of the proposed model in comparison to some generalized models (GMs).

  • 45.
    Karlsson Rosenblad, Andreas
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. Uppsala University, Sweden.
    The mean, variance, and bias of the OLS based estimator of the extremum of a quadratic regression model for small samples2022Ingår i: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 51, nr 9, s. 2870-2886Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many economic theories suggest that the relation between two variablesyandxfollow a function forming a convex or concave curve. In the classical linear model (CLM) framework, this function is usually modeled using a quadratic regression model, with the interest being to find the extremum value or turning point of this function. In the CLM framework, this point is estimated from the ratio of ordinary least squares (OLS) estimators of coefficients in the quadratic regression model. We derive an analytical formula for the expected value of this estimator, from which formulas for its variance and bias follow easily. It is shown that the estimator is biased without the assumption of normality of the error term, and if the normality assumption is strictly applied, the bias does not exist. A simulation study of the performance of this estimator for small samples show that the bias decreases as the sample size increases.

  • 46. Mensah, Aziz
    et al.
    Toivanen, Susanna
    Diewald, Martin
    ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Nyberg, Anna
    Workplace gender harassment, illegitimate tasks, and poor mental health: Hypothesized associations in a Swedish cohort2022Ingår i: Social Science and Medicine, ISSN 0277-9536, E-ISSN 1873-5347, Vol. 315, artikel-id 115520Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Workers exposed to gender harassment and illegitimate tasks may experience adverse mental health outcomessuch as depression and burnout. However, the longitudinal effects and the complex interrelationships betweenthese variables remain largely unexplored. We investigated the cross-lagged relationships between genderharassment, illegitimate tasks, and mental health outcomes among working adults in Sweden over a period oftwo years, as well as the gender differences in the cross-lagged effects. Additionally, the study examined whetherillegitimate tasks mediated the relationship between gender harassment and negative mental health outcomesover time. Data were drawn from the Swedish Longitudinal Occupational Survey of Health (SLOSH), covering2796 working men and 4110 working women in a two-wave analysis from 2018 to 2020. We employed astructural equation model to examine the cross-lagged effects and the mediating effect between genderharassment, illegitimate tasks, and mental health outcomes over time. Furthermore, we applied a multigroupanalysis to determine gender differences in the cross-lagged effects.The results showed statistically significant cross-lagged relationships (forward, reverse, and reciprocal) be-tween gender harassment, illegitimate tasks, and mental ill-health. There were statistically significant genderdifferences in these cross-lagged relationships (burnout: △χ2 (47) = 106.21, p < 0.01; depression: △χ2 (47) =80.5, p < 0.01). Initial illegitimate tasks mediated the relationship between gender harassment and mental ill-health outcomes over time. The gender differences in the interrelationships between gender harassment, ille-gitimate tasks, and mental ill-health outcomes among workers in Sweden indicate that policies, regulations, andinterventions that address these exposures in organisations must be tailored to benefit both men and women.

  • 47.
    Bueno, Edgar
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Hedlin, Dan
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    A method to find an efficient and robust sampling strategy under model uncertainty2021Ingår i: Survey Methodology, ISSN 0714-0045, E-ISSN 1492-0921, Vol. 47, nr 1, s. 75-89Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider the problem of deciding on sampling strategy, in particular sampling design. We propose a risk measure, whose minimizing value guides the choice. The method makes use of a superpopulation model and takes into account uncertainty about its parameters through a prior distribution. The method is illustrated with a real dataset, yielding satisfactory results. As a baseline, we use the strategy that couples probability proportional-to-size sampling with the difference estimator, as it is known to be optimal when the superpopulation model is fully known. We show that, even under moderate misspecifications of the model, this strategy is not robust and can be outperformed by some alternatives.