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  • 1. Fardos, Akbar
    et al.
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Jamal, Farrukh
    Ali, Hurria
    Noreen, Khadija
    Ahmed, Rashid
    Algorithm to generate efficient circular designs robust to neighbor effects2024In: Kuwait Journal of Science, ISSN 2307-4108, Vol. 51, no 1, article id 100135Article in journal (Refereed)
    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. Noreen, Khadija
    et al.
    Rashid, Muhammad Sajid
    Shehzad, Farrukh
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Noreen, Zahra
    Omer, Talha
    Ahmed, Rashid
    Algorithms to obtain generalized neighbor designs in minimal circular blocks2024In: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, Vol. 53, no 7, p. 3094-3105Article in journal (Refereed)
    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. 

  • 3. Wegmann, Bertil
    et al.
    Lundquist, Anders
    Eklund, Anders
    Villani, Mattias
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Bayesian modelling of effective and functional brain connectivity using hierarchical vector autoregressions2024In: The Journal of the Royal Statistical Society, Series C: Applied Statistics, ISSN 0035-9254, E-ISSN 1467-9876, Vol. 73, no 4, p. 835-856Article in journal (Refereed)
    Abstract [en]

    Analysis of brain connectivity is important for understanding how information is processed by the brain. We propose a novel Bayesian vector autoregression hierarchical model for analysing brain connectivity within resting-state functional magnetic resonance imaging, and apply it to simulated data and a real data set with subjects in different groups. Our approach models functional and effective connectivity simultaneously and allows for both group- and single-subject inference. We combine analytical marginalization with Hamiltonian Monte Carlo to obtain highly efficient posterior sampling. We show that our model gives similar inference for effective connectivity compared to models with a common covariance matrix to all subjects, but more accurate inference for functional connectivity between regions compared to models with more restrictive covariance structures. A Stan implementation of our model is available on GitHub.

  • 4.
    Ghilagaber, Gebrenegus
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Bayesian Ordinal Modeling of Educational Attainment among Five Cohorts of Ethiopian Women: An Example of Unequal Variances and Category-Specific Effects2024Conference paper (Other academic)
  • 5.
    Ghilagaber, Gebrenegus
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Bayesian Ordinal Modeling of Effects of Online Teaching During the COVID-19 Pandemic Lockdown on Students with Disabilities2024Conference paper (Other academic)
  • 6.
    Andersson, Per Gösta
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Confidence Interval for a Binomial p: Recommend the Wilson Interval to Students2024In: CHANCE: New Directions for Statistics and Computing, ISSN 0933-2480, Vol. 37, no 2, p. 13-15Article in journal (Refereed)
    Abstract [en]

    The Wald confidence interval for a binomial p should be completely gone by now from teaching as the interval to present and recommend. In reality, this unfortunately not so. This article makes a strong case for instead introducing the Wilson interval even in a first course in statistical inference.

  • 7. Riaz, Muhammad
    et al.
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Tahir, M. H.
    Rasheed, H. M. Kashif
    Khan, Abid
    Ahmed, Rashid
    Construction of efficient classes of circular balanced repeated measurements designs with R2024In: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415XArticle in journal (Refereed)
    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.

  • 8. Rasheed, H. M. Kashif
    et al.
    Khan, Abid
    Noreen, Khadija
    Salam, Abdul
    Hussain, Sajid
    Ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Ahmed, Rashid
    Efficient circular repeated measurements designs strongly balanced to control carryover effects2024In: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141Article in journal (Refereed)
    Abstract [en]

    In experiments related to agriculture, psychology, medicine, animal sciences, pharmacology, and other fields, repeated measurements designs (RMDs) are utilized which are economical design. However, the use of these designs may result in carryover effects, which are the primary cause of bias. Balanced or strongly balanced RMDs can control these effects. Strongly balanced RMDs estimate the direct effects and carryover effects independently; therefore, these designs have an edge over the balanced RMDs. In this article, therefore, some general procedures are presented to obtain minimal circular strongly and nearly strongly balanced RMDs in periods of k different sizes with high efficiency of Separability and of carryover effects.

  • 9. Jabeen, Rida
    et al.
    Khan, Abid
    Rasheed, H. M. Kashif
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Ahmed, Rashid
    General construction of efficient circular partially strongly-balanced repeated measurements designs2024In: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, Vol. 53, no 5, p. 2461-2471Article in journal (Refereed)
    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. 

  • 10.
    Oelrich, Oscar
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Villani, Mattias
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Ankargren, Sebastian
    Local prediction pools2024In: Journal of Forecasting, ISSN 0277-6693, E-ISSN 1099-131X, p. 103-117Article in journal (Refereed)
    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.

  • 11. Sallnäs Pysander, Eva-Lotta
    et al.
    Mårtensson, Fredrika
    Waern, Annika
    Litsmark, Anna
    Hedblom, Marcus
    Raustorp, Anders
    Ghilagaber, Gebrenegus
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Zhu, Hui
    Nature and digitalisation challenging the traditional playground2024In: Urban Forestry & Urban Greening, ISSN 1618-8667, E-ISSN 1610-8167, Vol. 93, article id 128148Article in journal (Refereed)
    Abstract [en]

    Playing outdoors in nature with peers has been attributed most importance for children's healthy development but is increasingly marginalized because of the attractiveness of screen-based play. Careful merging of digital technology into outdoor play environments rich on nature elements 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 behavior was evaluated using a behavioral 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 behavior 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. 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.

  • 12. Agneessens, Filip
    et al.
    Trincado-Munoz, Francisco J.
    Koskinen, Johan
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Network formation in organizational settings: Exploring the importance of local social processes and team-level contextual variables in small groups using bayesian hierarchical ERGMs2024In: Social Networks, ISSN 0378-8733, E-ISSN 1879-2111, Vol. 77, p. 104-117Article in journal (Refereed)
    Abstract [en]

    Statistical models for social networks, such as exponential random graphs (ERGMs), have increasingly been used by organizational scholars to study the social interactions inside organizations, departments, and teams. While such models have been successful in providing insights about the local processes that underlie these interactions (such as homophily, reciprocity or transitivity), an additional interesting avenue for research focuses on the role of group-level contextual variables (such as the climate or composition of a team or organization) when considering a multitude of teams or organizations. In this paper we show how, in a team context, integrating team-level factors in a multilevel framework (i.e., a Bayesian hierarchical ERGM) enables us to answer questions about: 1) how team-level contextual factors might provide alternative explanations for the emergence of intra-team ties, and 2) whether any variation in local tendencies between teams might be dependent on such team-level variables (i.e., cross-level interactions). Using data collected among 103 MBA students who were grouped into 18 teams of 5–7 members to work on a project, we study the impact of members’ expertise and perceived psychological safety on advice seeking behavior. At a local level, we focus on the effect of these nodal attributes for homophily and differences in advice seeking and giving, while at the team level we incorporate the average expertise and the team’s psychological safety climate. Our results show that expert members are more likely to be the recipient of advice ties, but also that this effect is more pronounced in teams where the overall level of expertise is high. For psychological safety, we find that a high psychological safety climate impacts the advice relations among all members in the group, not solely those who themselves perceive a high level of psychological safety, suggesting that the team climate has an impact on all its members. This illustrates how a Bayesian hierarchical ERGM allows us to obtain relevant results even when studying small-sized groups

  • 13.
    Chizarifard, Azadeh
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    On Estimation and Prediction in Linear Mixed Models: A new approach to studying equal BLUEs and BLUPs2024Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Linear mixed models (LMMs) are widely used to analyze repeated, longitudinal, or clustered data in many disciplines, such as biology, medicine, psychology, sociology, economics, etc. One of the essential components of a linear mixed model is its covariance structure, i.e., the covariance matrices of the random part and the error part, respectively, and the relationship between them. Specifying the covariance structure can be very challenging in a given situation. An important issue concerns the best linear unbiased estimators (BLUE) and the best linear unbiased predictors (BLUPs) under a given LMM and if two LMMs with different covariance structures generate equal BLUEs and/or BLUPs.

    This thesis proposes a new approach to determine the equality of the BLUEs and the BLUPs of the fixed and random effects under two linear mixed models with different covariance structures, and we present straightforward criteria to evaluate conditions that lead to equal BLUEs and BLUPs under these two models.  

    Papers I and II focus on the equality of the BLUEs, while Papers II and IV study equal BLUPs under two LMMs with different covariance structures. More specifically, Paper I considers two different LMMs concerning their covariance matrices and whether the models generate equal BLUEs. In Paper II, we study the conditions for invariant BLUEs under a partitioned linear fixed effects model and a corresponding linear mixed model. Paper III develops the results to obtain the common BLUPs under two LMMs considering uncorrelated random effects and random errors. Finally, Paper IV extends the results of Paper III to obtain equal BLUPs in two linear mixed models, allowing for a correlation between the random effects and the random errors.

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  • 14.
    Ul Hassan, Mahmood
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics. Karolinska Institute, Sweden.
    Miller, Frank
    Stockholm University, Faculty of Social Sciences, Department of Statistics. Linköping University, Sweden.
    Optimal Calibration of Items for Multidimensional Achievement Tests2024In: Journal of educational measurement, ISSN 0022-0655, E-ISSN 1745-3984, Vol. 61, no 2, p. 274-302Article in journal (Refereed)
    Abstract [en]

    Multidimensional achievement tests are recently gaining more importance in educational and psychological measurements. For example, multidimensional diagnostic tests can help students to determine which particular domain of knowledge they need to improve for better performance. To estimate the characteristics of candidate items (calibration) for future multidimensional achievement tests, we use optimal design theory. We generalize a previously developed exchange algorithm for optimal design computation to the multidimensional setting. We also develop an asymptotic theorem saying which item should be calibrated by examinees with extreme abilities. For several examples, we compute the optimal design numerically with the exchange algorithm. We see clear structures in these results and explain them using the asymptotic theorem. Moreover, we investigate the performance of the optimal design in a simulation study. 

  • 15.
    Miller, Frank
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics. Linköping University, Sweden.
    Fackle-Fornius, Ellinor
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Parallel Optimal Calibration of Mixed-Format Items for Achievement Tests2024In: Psychometrika, ISSN 0033-3123, E-ISSN 1860-0980Article in journal (Refereed)
    Abstract [en]

    When large achievement tests are conducted regularly, items need to be calibrated before being used as operational items in a test. Methods have been developed to optimally assign pretest items to examinees based on their abilities. Most of these methods, however, are intended for situations where examinees arrive sequentially to be assigned to calibration items. In several calibration tests, examinees take the test simultaneously or in parallel. In this article, we develop an optimal calibration design tailored for such parallel test setups. Our objective is both to investigate the efficiency gain of the method as well as to demonstrate that this method can be implemented in real calibration scenarios. For the latter, we have employed this method to calibrate items for the Swedish national tests in Mathematics. In this case study, like in many real test situations, items are of mixed format and the optimal design method needs to handle that. The method we propose works for mixed-format tests and accounts for varying expected response times. Our investigations show that the proposed method considerably enhances calibration efficiency.

  • 16. Pedrana, Alisa
    et al.
    Koskinen, Johan
    Stockholm University, Faculty of Social Sciences, Department of Statistics. The University of Melbourne, Australia.
    Hellard, Margaret
    Priority populations’ experiences of isolation, quarantine and distancing for COVID-19: protocol for a longitudinal cohort study (Optimise Study)2024In: BMJ Open, E-ISSN 2044-6055, Vol. 14, no 1, article id e076907Article in journal (Refereed)
    Abstract [en]

    Introduction Longitudinal studies can provide timely and accurate information to evaluate and inform COVID-19 control and mitigation strategies and future pandemic preparedness. The Optimise Study is a multidisciplinary research platform established in the Australian state of Victoria in September 2020 to collect epidemiological, social, psychological and behavioural data from priority populations. It aims to understand changing public attitudes, behaviours and experiences of COVID-19 and inform epidemic modelling and support responsive government policy.

    Methods and analysis This protocol paper describes the data collection procedures for the Optimise Study, an ongoing longitudinal cohort of ~1000 Victorian adults and their social networks. Participants are recruited using snowball sampling with a set of seeds and two waves of snowball recruitment. Seeds are purposively selected from priority groups, including recent COVID-19 cases and close contacts and people at heightened risk of infection and/or adverse outcomes of COVID-19 infection and/or public health measures. Participants complete a schedule of monthly quantitative surveys and daily diaries for up to 24 months, plus additional surveys annually for up to 48 months. Cohort participants are recruited for qualitative interviews at key time points to enable in-depth exploration of people’s lived experiences. Separately, community representatives are invited to participate in community engagement groups, which review and interpret research findings to inform policy and practice recommendations.

  • 17.
    Öhrstedt, Maria
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Education.
    Käck, Annika
    Stockholm University, Faculty of Social Sciences, Department of Special Education.
    Reierstam, Helena
    Stockholm University, Faculty of Social Sciences, Department of Education.
    Ghilagaber, Gebrenegus
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Studying online with special needs: a student perspective2024In: Journal of Research in Special Educational Needs, E-ISSN 1471-3802Article in journal (Refereed)
  • 18. Xiao, Yinshuang
    et al.
    Cui, Yaxin
    Raut, Nikita
    Januar, Jonathan
    Koskinen, Johan
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Contractor, Noshir
    Chen, Wei
    Sha, Zhenghui
    Survey data on customer two-stage decision-making process in household vacuum cleaner market2024In: Data in Brief, E-ISSN 2352-3409, Vol. 54, article id 110353Article in journal (Refereed)
    Abstract [en]

    This paper presents the data collection method and introduces the dataset about consumers’ consider-then-choose behaviors in the household vacuum cleaner market. First, we designed a questionnaire that collected participants’ consideration and choice data, social network data, demographic information, and preferences for product features. In addition, we obtained data on vacuum cleaner product features through web scraping from online shopping websites. After data cleaning and processing, the resulting dataset enables investigation into customer preferences in two stages, namely the consideration and choice stages and the impact of social influence on the two-stage decision-making process. This dataset is unique as it is the first of its kind to collect both customers’ revealed preferences in a two-stage decision-making process and their ego social networks. This enables the modeling of customer preferences while accounting for social influence. The published survey questionnaire can be used as a template to collect data on other products in support of customer preferences modeling and the design for market systems.

  • 19. Armelius, Hanna
    et al.
    Solberger, Martin
    Spånberg, Erik
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Österholm, Pär
    The evolution of the natural rate of interest: evidence from the Scandinavian countries2024In: Empirical Economics, ISSN 0377-7332, E-ISSN 1435-8921, Vol. 66, no 4, p. 1633-1659Article in journal (Refereed)
    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. 

  • 20.
    Hlynsson, Jón Ingi
    et al.
    Stockholm University.
    Gustafsson, Oskar
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Carlbring, Per
    Stockholm University, Faculty of Social Sciences, Department of Psychology, Clinical psychology.
    Uncertainty breeds anxiety and depression: The impact of the Russian invasion in Ukraine on a Swedish clinical population receiving internet-based psychotherapy2024In: Clinical Psychology in Europe, E-ISSN 2625-3410, Vol. 6, no 1, article id e12083Article in journal (Refereed)
    Abstract [en]

    Background: Recent global crises, such as the COVID-19 pandemic and the 2022 Russian invasion of Ukraine, have contributed to a rise in the global prevalence of anxiety and depressive disorders. This study examines the indirect impact of the Ukraine war on emotional disorders within a Swedish clinical population. Method: The sample comprised participants (n = 1,222) actively engaged in an internet-based psychotherapeutic intervention (cognitive-behavioral, psychodynamic, and waitlist) when the war broke out. The Patient Health Questionnaire-9 scale and the Generalized Anxiety Disorder-7 scale were used to measure depression and anxiety. Results: Anxiety and depressive symptom severity increased following the war's onset, with an average weekly increase of 0.77-points for anxiety (p = .001, Cohen's d = 0.08) and 0.09-points for depression (p = .70, Cohen's d = 0.01); however, the increase was negligible for depression. Furthermore, higher socioeconomic status (SES) predicted declines in depression and anxiety during the study period, with a 0.69-point average weekly decrease in anxiety (p < .001, Cohen's d = 0.32) and a 1.09-point decrease in depression (p < .001, Cohen's d = 0.48) per one unit increase in SES, suggesting that SES may serve as a protective factor that buffers against psychopathological development during crises. Conclusions: These findings have implications for mitigating the development of psychopathology during crises and interpreting treatment efficacy estimates during such events. Our findings also emphasize the potential of internet-based psychotherapy in addressing emotional disorders during crises. This study presents up-to-date information about the reaction of treatment-seeking individuals to abrupt uncertainty.

  • 21.
    Ghilagaber, Gebrenegus
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Larsson, Rolf
    Adjustment of Anticipatory Covariates in Retrospective Surveys: An Expected Likelihood Approach2023In: Stats, ISSN 2571-905X, Vol. 6, no 4, p. 1179-1197Article in journal (Refereed)
    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.

  • 22. Shabbir, Javid
    et al.
    Hassan, Jamshaid ul
    Ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Noreen, Khadija
    Hussain, Sajid
    Ahmed, Rashid
    An Algorithm Coded with R to Generate GN2-designs in Circular Blocks2023In: VFAST Transactions on Mathematics, ISSN 2411-6343, Vol. 11, no 2, p. 16-27Article in journal (Refereed)
    Abstract [en]

    Minimal neighbor balanced designs are economical, therefore, these are preferred by the experimenters to minimize the bias due to neighbor effects. Minimal circular balanced neighbor designs cannot be constructed for almost every case of even, where is number of the treatments to be compared. For even, the circular GN2-designs in which each treatment appears exactly once as neighbors with all other treatments except the one with which it appears twice, are considered the better alternate to the minimal balanced neighbor designs. In this article, an algorithm is developed to generate the circular GN2-designs for v even which can be converted directly into minimal circular balanced and strongly balanced neighbor designs. This algorithm is also coded with R.

  • 23.
    Koskinen, Johan
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics. The Melbourne School of Psychological Sciences, Australia.
    Jones, Pete
    Medeuov, Darkhan
    Antonyuk, Artem
    Puzyreva, Kseniia
    Basov, Nikita
    Analysing networks of networks2023In: Social Networks, ISSN 0378-8733, E-ISSN 1879-2111, Vol. 74, p. 102-117Article in journal (Refereed)
    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.

  • 24.
    Ghilagaber, Gebrenegus
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Bayesian Change Point Analysis of Levels and Trends in Total Fertility Rates in Africa, 1960–20202023In: / [ed] Population Association of America, 2023Conference paper (Refereed)
  • 25.
    Gustafsson, Oskar
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Villani, Mattias
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Stockhammar, Pär
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Bayesian optimization of hyperparameters from noisy marginal likelihood estimates2023In: Journal of applied econometrics (Chichester, England), ISSN 0883-7252, E-ISSN 1099-1255, Vol. 38, no 4, p. 577-595Article in journal (Refereed)
    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.

  • 26.
    Ghilagaber, Gebrenegus
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Fenialdi, Elena
    Bayesian Piecewise Exponential Modeling of Environmental Recidivism in Sweden2023In: / [ed] Population Association of America, 2023Conference paper (Other academic)
  • 27. Hassan, Jamshaidul
    et al.
    Noreen, Khadija
    Rasheed, H. M. Kashif
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Ahmed, Rashid
    Construction of circular quasi rees neighbor designs which can be converted into minimal circular balanced and strongly balanced neighbor designs2023In: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 52, no 16, p. 5587-5605Article in journal (Refereed)
    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.

  • 28. Khan, Abid
    et al.
    Bashir, Zahid
    Rasheed, H. M. Kashif
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Ahmed, Rashid
    Construction of minimal circular nearly strongly balanced repeated measurements designs and their conversion2023In: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, Vol. 52, no 12, p. 5749-5758Article in journal (Refereed)
    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.

  • 29.
    Munezero, Parfait
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics. Ericsson, Stockholm, Sweden.
    Villani, Mattias
    Stockholm University, Faculty of Social Sciences, Department of Statistics. Linköping University, Linköping, Sweden.
    Kohn, Robert
    Dynamic Mixture of Experts Models for Online Prediction2023In: Technometrics, ISSN 0040-1706, E-ISSN 1537-2723, Vol. 65, no 2, p. 257-268Article in journal (Refereed)
    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. 

  • 30. Holle, Hannah
    et al.
    Ghilagaber, Gebrenegus
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Drees, Randi
    Evaluation of the normal gastrointestinal tract in cats using dual-phase computed tomography2023In: Journal of Small Animal Practice, ISSN 0022-4510, E-ISSN 1748-5827, Vol. 64, no 7, p. 463-476Article in journal (Refereed)
    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.

  • 31. Hussain, Sajid
    et al.
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Rashid, Muhammad Sajid
    Ahmed, Rashid
    Families of Extended Exponentiated Generalized Distributions and Applications of Medical Data Using Burr III Extended Exponentiated Weibull Distribution2023In: Mathematics, E-ISSN 2227-7390, Vol. 11, no 14, article id 3090Article in journal (Refereed)
    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.

  • 32.
    Hedlin, Dan
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Formal sensitivity analysis in observational studies2023Report (Other academic)
    Abstract [en]

    Objective: The positive effect of antidiabetic medication on cognitive decline has been given some support by, among others, Secnik et al (2021) and Secnik et al (2022). However, as they are observational studies, it is not clear whether the effect is causal.

    Research design and methods: Using the Swedish Dementia Registry and supplementary Swedish registers/databases, we identified 1,873 patients (4,732 observations) with diagnosis of diabetes and Alzheimer’s disease or mixed-pathology dementia who were followed-up at least once after dementia diagnosis. The association of use of metformin with Mini-Mental State Examination scores in patients with diabetes and dementia was studied in two ways. 1) The difference between the last and the first score for each patient was compared with treatment (use of metformin) and subjected to a new sensitivity analysis. 2) The difference between scores for each patient at the points in time when there was a change in use of metformin (either start of use, or discontinuation of use) was studied.

    Results: There is an association between cognitive decline and use of metformin. However, any conclusion of a causal relationship is tenuous. 

    Conclusion: The present study offers no basis for causal conclusions, but given the association, further examination of cognitive effects of metformin is warranted.

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  • 33.
    Quiroz, Matias
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics. ARC Centre of Excellence for Mathematical and Statistical Frontiers (ACEMS), Australia.
    Nott, David J.
    Kohn, Robert
    Gaussian Variational Approximations for High-dimensional State Space Models2023In: Bayesian Analysis, ISSN 1936-0975, E-ISSN 1931-6690, Vol. 18, no 3, p. 989-1016Article in journal (Refereed)
    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.

  • 34.
    Daw, Tim M.
    et al.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Reid, Nicole J.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Coulthard, Sarah
    Chaigneau, Tomas
    Machava Antonio, Vilma
    Cheupe, Christopher
    Wells, Geoff J.
    Stockholm University, Faculty of Science, Stockholm Resilience Centre.
    Bueno, Edgar
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Life satisfaction in coastal Kenya and Mozambique reflects culture, gendered relationships and security of basic needs: Implications for ecosystem services2023In: Ecosystem Services, E-ISSN 2212-0416, Vol. 62, article id 101532Article in journal (Refereed)
    Abstract [en]

    Life satisfaction is both a desirable 'end' for sustainable development, and a means to understand the priorities, and behaviour of people towards local ecosystems. Ecosystem-services research on life satisfaction has focused on cultural services in wealthy, Western contexts, although ecosystem services are essential for poor people's livelihoods in the Global South. We examined reported life satisfaction from a survey of over 2000 people in rural and urban settings of coastal Kenya and Mozambique. We coded respondents' open-ended reasons for their reported satisfaction, and used multiple correspondence analysis to explore the characteristics of people who mentioned different reasons. We tested associations between satisfaction and the meeting of basic needs and income, with binary logistic regression, accounting for site and gender. Life satisfaction was lower in Kenya, for men, and in the most urbanised site. Respondents explained high, and low, satisfaction in terms of social relationships, basic needs, money and employment. They rarely mentioned the ecosystem services and related livelihoods that underpin those, suggesting an instrumental relation to nature. Meeting basic needs, including economic security better predicted satisfaction than household income. Life satisfaction reflected material differences in people's lives but also different evaluative criteria and national cultures. For example, family reasons more commonly explained women's satisfaction, while money was more important for urban-dwelling men. We propose that the holistic perspective offered by life-satisfaction research can inform environmental management alongside more focused ecosystem-service research. For example, our results suggest that a) interventions should recognise immediate needs and social relationships, b) the role of ecosystem services for subjective wellbeing varies by local culture and individual identities and c) secure and fair access to ecosystem services may support life satisfaction better than high incomes that are insecure or ineq-uitably distributed.

  • 35.
    Koskinen, Johan
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Snijders, Tom A B
    Multilevel longitudinal analysis of social networks2023In: Journal of the Royal Statistical Society: Series A (Statistics in Society), ISSN 0964-1998, E-ISSN 1467-985X, Vol. 186, no 3, p. 376-400Article in journal (Refereed)
    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.

  • 36. Robins, Garry
    et al.
    Lusher, Dean
    Broccatelli, Chiara
    Bright, David
    Gallagher, Colin
    Karkavandi, Maedeh Aboutalebi
    Matous, Petr
    Coutinho, James
    Wang, Peng
    Koskinen, Johan
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Roden, Bopha
    Sadewo, Giovanni Radhitio Putra
    Multilevel network interventions: Goals, actions, and outcomes2023In: Social Networks, ISSN 0378-8733, E-ISSN 1879-2111, Vol. 72, p. 108-120Article in journal (Refereed)
  • 37. Gallagher, Colin
    et al.
    Lusher, Dean
    Koskinen, Johan
    Stockholm University, Faculty of Social Sciences, Department of Statistics. 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 Australia2023In: Scientometrics, ISSN 0138-9130, E-ISSN 1588-2861, Vol. 128, no 8, p. 4559-4588Article in journal (Refereed)
    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.

  • 38. Nadeem, Muhammad
    et al.
    Noreen, Khadija
    Kashif Rasheed, H. M.
    Ahmed, Rashid
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    New generators for minimal circular generalised neighbour designs in blocks of two different sizes2023In: Statistics in Transition New Series, ISSN 1234-7655, Vol. 24, no 2, p. 85-92Article in journal (Refereed)
    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. 

  • 39.
    Tsirpitzi, Renata Eirini
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Miller, Frank
    Stockholm University, Faculty of Social Sciences, Department of Statistics. Linköping University, Sweden.
    Burman, Carl-Fredrik
    Robust optimal designs using a model misspecification term2023In: Metrika (Heidelberg), ISSN 0026-1335, E-ISSN 1435-926X, no 86, p. 781-804Article in journal (Refereed)
    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. 

  • 40.
    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
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Ahmed, Rashid
    The Islamia University of Bahawalpur, Bahawalpur, Pakistan.
    Some important classes of non-directional minimal circular weakly balanced neighbor designs2023In: Communications in statistics. Simulation and computation, ISSN 0361-0918, E-ISSN 1532-4141, p. 1-10Article in journal (Refereed)
    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.

  • 41.
    Jederlund, Ulf
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Special Education.
    von Rosen, Tatjana
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Teacher-student relationships and students' self-efficacy beliefs. Rationale, validation and further potential of two instruments2023In: Education Inquiry, E-ISSN 2000-4508, Vol. 14, no 4, p. 529-553Article in journal (Refereed)
    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.   

  • 42. Hussain, Sajid
    et al.
    ul Hassan, Mahmood
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Sajid Rashid, Muhammad
    Ahmed, Rashid
    The Exponentiated Power Alpha Index Generalized Family of Distributions: Properties and Applications2023In: Mathematics, E-ISSN 2227-7390, Vol. 11, no 4, p. 900-900Article in journal (Refereed)
    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.

  • 43. Ahmed, Imaduddin
    et al.
    Parikh, Priti
    Munezero, Parfait
    Stockholm University, Faculty of Social Sciences, Department of Statistics. Ericsson, Sweden.
    Sianjase, Graham
    Coffman, D'Maris
    The impact of power outages on households in Zambia2023In: Economia Politica, ISSN 1120-2890, E-ISSN 1973-820X, no 40, p. 835-867Article in journal (Refereed)
    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.

  • 44.
    Andersson, Per Gösta
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    The Wald Confidence Interval for a Binomial p as an Illuminating “Bad” Example2023In: American Statistician, ISSN 0003-1305, E-ISSN 1537-2731, Vol. 77, no 4, p. 443-448Article in journal (Refereed)
    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. 

  • 45. Rodriguez-Deniz, Hector
    et al.
    Villani, Mattias
    Stockholm University, Faculty of Social Sciences, Department of Statistics. Linköping University, Sweden.
    Voltes-Dorta, Augusto
    A multilayered block network model to forecast large dynamic transportation graphs: An application to US air transport2022In: Transportation Research Part C: Emerging Technologies, ISSN 0968-090X, E-ISSN 1879-2359, Vol. 137, article id 103556Article in journal (Refereed)
    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.

  • 46.
    Lachmann, Jon
    et al.
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Storvik, Geir
    Frommlet, Florian
    Hubin, Aliaksandr
    A subsampling approach for Bayesian model selection2022In: International Journal of Approximate Reasoning, ISSN 0888-613X, E-ISSN 1873-4731, Vol. 151, p. 33-63Article in journal (Refereed)
    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. 

  • 47.
    Andersson, Per Gösta
    Stockholm University, Faculty of Social Sciences, Department of Statistics.
    Approximate Confidence Intervals for a Binomial p—Once Again2022In: Statistical Science, ISSN 0883-4237, E-ISSN 2168-8745, Vol. 37, no 4, p. 598-606Article in journal (Refereed)
    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.

  • 48. Söderström, Lisa
    et al.
    Forslund, Marina
    Johansson, Birgitta
    Ottenblad, Anna
    Rosenblad, Andreas
    Stockholm University, Faculty of Social Sciences, Department of Statistics. 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 radiotherapy2022In: Upsala Journal of Medical Sciences, ISSN 0300-9734, E-ISSN 2000-1967, Vol. 127, no 1, article id e8261Article in journal (Refereed)
    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.

  • 49. Liang, Yuli
    et al.