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  • 151.
    Grünewald, Maria
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen. Matematisk statistik.
    Humphreys, Keith
    A Stochastic EM type algorithm for estimation in data with ascertainment on continuous outcomes2008Rapport (Annet vitenskapelig)
    Abstract [en]

    Outcome dependent sampling probabilities can be used to increase efficiency in observational studies. For continuous outcomes appropriate consideration of sampling design in estimating parameters of interest is often computationally cumbersome. In this article we suggest a Stochastic EM type algorithm for estimation. The computational complexity of the likelihood is avoided by filling in missing data so that the full data likelihood can be used. The method is not restricted to any specific distribution of the data and can be used for a broad range of statistical models.

  • 152.
    Grünewald, Maria
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Humphreys, Keith
    Karolinska institutet.
    Hössjer, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    A Stochastic EM Type Algorithm for Parameter Estimation in Models with Continuous Outcomes, under Complex Ascertainment2010Inngår i: The International Journal of Biostatistics, ISSN 1557-4679, E-ISSN 1557-4679, Vol. 6, nr 1, s. Article 23-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Outcome-dependent sampling probabilities can be used to increase efficiency in observational studies. For continuous outcomes, appropriate consideration of sampling design in estimating parameters of interest is often computationally cumbersome. In this article, we suggest a Stochastic EM type algorithm for estimation when ascertainment probabilities are known or estimable. The computational complexity of the likelihood is avoided by filling in missing data so that an approximation of the full data likelihood can be used. The method is not restricted to any specific distribution of the data and can be used for a broad range of statistical models. 

  • 153.
    Grünewald, Maria
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Hössjer, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    A General Statistical Framework for Multistage Designs2010Manuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The efficiency of observational studies may be increased by applying multistage sampling designs. It is however not always transparent how to construct such a design in order to obtain increased efficiency. We here present a general statistical framework for describing and con- structing multistage designs. We also provide tools for efficiency and cost-efficiency comparisons, to facilitate the choice of sampling scheme. The comparisons are based on Fisher information matrices and the results are suggested being presented in graphs, where either efficiency or cost adjusted efficiency is plotted against a normalized measure of cost. The former curve resides in the unit square and is analogous to the receiver operating characteristic curve used for testing.

     

  • 154.
    Grünewald, Maria
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Hössjer, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Efficient ascertainment schemes for maximum likelihood estimation2010Inngår i: Journal of Statistical Planning and Inference, ISSN 0378-3758, E-ISSN 1873-1171, Vol. 140, nr 7, s. 2078-2088Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A well chosen sampling scheme can substantially increase the efficiency of a study. However, it is not always obvious how to sample well. Neyman (1938) presents the possibility of two-stage sampling to increase efficiency in field sampling, and concludes that two-stage sampling sometimes, but not always, reduces the variance of estimates of means. Since then various authors have investigated the effects of two-stage and multistage sampling in different settings, most of which focus on binary outcome variables. In some special cases, such as case-control studies, there are rules of thumb to follow with regards to efficiency, see for example Maydrech and Kupper (1978), but in most other settings more elaborate calculations are necessary to discriminate between different options. Multistage sampling is described in the context of genetic epidemiology by, among others, Whittemore and Halpern (1997): Case-control status of prostate cancer is first ascertained and then more expensive measures such as family history of disease and DNA samples are collected. Asymptotic variances of Horvitz–Thompson estimates are derived. Reilly (1996) investigates optimal allocation of available resources for two-stage data with binary outcomes. Complete information is there available from variables sampled in Stage 1, while Stage 2 variables are sampled more sparsely with probabilities determined by Stage 1 data. Cost is allowed to differ between sampling in Stage 1 and sampling in Stage 2. The author emphasizes the usefulness of pilot studies to obtain information needed to find the optimal allocation. Zhou et al. (2007) investigate outcome dependent sampling where the outcome variable is continuous. Power of tests based on a semi-parametric estimator are compared with the power of an inverse probability weighted estimator and the power of a maximum likelihood estimator based on a simple random sample. 

  • 155.
    Guilbaud, Olivier
    Stockholms universitet.
    Nonparametric statistical inference about location: some contributions1978Doktoravhandling, med artikler (Annet vitenskapelig)
  • 156.
    Gustafsson, Oskar
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Stockhammar, Pär
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen. National Institute of Economic Research (NIER), Sweden.
    Variance stabilizing filters2019Inngår i: Communications in Statistics - Theory and Methods, ISSN 0361-0926, E-ISSN 1532-415X, Vol. 48, nr 24, s. 6155-6168Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper new filters for removing unspecified form of heteroscedasticity are proposed. The filters build on the assumption that the variance of a pre-whitened time series can be viewed as a latent stochastic process by its own. This makes the filters flexible and useful in many situations. A simulation study shows that removing heteroscedasticity before fitting a model leads to efficiency gains and bias reductions when estimating the parameters of ARMA models. A real data study shows that pre-filtering can increase the forecasting precision of quarterly US GDP growth.

  • 157.
    Hagberg, Jan
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    On Degree Variance in Random Graphs2004Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    This thesis is concerned with degree moments and degree variance in random graphs. The degree of vertex i in a graph is the number of edges incident to vertex i.

    In the first paper, degree moments and functions of degree moments are investigated for three random graph models. In statistical applications of random graph models the degree moments, and functions of the degree moments, have been found useful both as summary statistics and for inference on particular random graph models. Exact and asymptotic formulas are given for various degree statistics, in particular the degree variance.

    The second paper focus on the degree variance. Exact and asymptotic distributions of the degree variance are investigated for Bernoulli graphs and uniform random graphs. For graphs of large order, we show that the degree variance is approximately gamma distributed with parameters obtained from the first two moments of the degree variance. The usefulness of the results is illustrated by a graph centrality test with a critical value obtained from the gamma distribution.

    The third and last paper is concerned with extreme values and other attained values of the degree variance among graphs of fixed order and size, and among graphs of fixed order. The structure of the extreme graphs is investegated and it is shown that the maximum value of the degree variance can be obtained from integer sequences associated to the triangular numbers. Explicite formulas for the number of possible values and recurrence relations for the attained values of the degree variance are developed.

  • 158.
    Hammarlid, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Large deviation techniques applied to three questions of when ...2005Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Large deviation techniques are used to solve three problems; when is a distant convex barrier passed, when to accept a sequence of gambles and when is the time of ruin. This work is the collection of four papers.

    Paper I: When is a convex barrier passed for the first time by a random walk? With a certain scaling, the limit distribution of the first passage time to a convex barrier decays exponentially in the scale parameter. Under the Esscher transform, which changes the drift, four properties are proved. First, the limit distribution of the overshoot is distributed as an overshoot over a linear barrier. Secondly, the stopping time is asymptotically normally distributed when it is properly normalized. Thirdly, the overshoot and the asymptotic normal part are asymptotically independent. Fourthly, the overshoot over a linear barrier is bounded by an exponentially distributed random variable. The combination of these building blocks gives the function that multiplies the exponential part in the asymptotic distribution.

    Paper II: This paper continues the work on first passage times to a convex barrier. The rate of exponential decay changes for times before the most probable passage time. The function multiplying the exponential part also alters to a constant divided by the square root of the scale parameter. An auxiliary result used in the proof of this is the characteristic function of the stopping time which decays exponentially in its non-central parts.

    Paper III: A sequence of gambles which initially is rejected, is eventually accepted when the gambles follow a large deviation principle and the utility function is non-satiated and bounded from below in a certain way. The number of gambles required for acceptance is computed.

    Paper IV: In classical risk theory, the surplus can increase to infinity. This is however not realistic in real life. To get a more applicable model, a variable premium that depends on the level of the surplus is introduced. The variable premium is assumed to be linear such that the buffer is a generalized Ornstein-Uhlenbeck process. Asymptotically, the time to ruin with a certain scaling is shown to be exponentially distributed.

  • 159.
    Hansson, Disa
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Hidden desires: Modelling sexual behaviour and the spread of sexually transmitted infections2017Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis we use statistical and mathematical models to study different sexual behaviours of relevance for the spread of sexually transmitted infections (STIs). Two groups of special interest for STI interventions are considered: sexually active youths and men who have sex with men (MSM). The focus of the first paper is on mechanisms giving rise to the observed condom use and anal sex behaviour among young people in Sweden. We study the sexual dispositions of individuals, how these interact and generate the observed sexual outcome. The second paper concerns the sexual behaviour of MSM in Sweden and the transmission process of HIV within this population. The population is modelled by a stochastic dynamic network which incorporates both steady partnerships and casual contacts. We model the spread of an infection where individuals are susceptible, infectious, or diagnosed (and unable to transmit) and derive the basic reproduction number R0, the probability of a major outbreak and the endemic prevalence.

  • 160.
    Hansson, Disa
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Modelling Sexual Interactions: Sexual behaviour and the spread of sexually transmitted infections on dynamic networks2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis we develop statistical and mathematical models to study different factors of relevance for the spread of sexually transmitted infections (STIs). Two special interest groups for STI interventions are considered: sexually active youths and men who have sex with men (MSM). The statistical models developed make it possible to estimate individuals’ dispositions towards sexual behaviours related to the spread of STIs: condom use and anal sex. To study the spread of an infection in a population we use mathematical models. The mathematical models in this thesis give insights into the transmission process of HIV among MSM in Sweden—a population at high risk for HIV infection.

    The focus of the first paper is on mechanisms giving rise to observed sexual behaviour, such as condom use, among sexually active youths in Sweden. We study the sexual dispositions of individuals and how these interact and generate the observed sexual outcomes.

    The second paper concerns the sexual behaviour of MSM in Sweden and the transmission process of HIV within this population. The population is modelled by a stochastic dynamic network model that incorporates both steady partnerships and casual contacts. We model the spread of an infection where individuals are susceptible, infectious or diagnosed (unable to transmit) and derive the basic reproduction number R0, the probability of a major outbreak, and the endemic prevalence.

    The third paper further develops the dynamic network model of the second paper. The model now takes into account that individuals may be sexually high-active or sexually low-active. The division into two activity groups makes it possible to study a preventive intervention against HIV that is only targeted to sexually high-active. The intervention studied is pre-exposure prophylaxis for HIV (PrEP), i.e. that the antiviral drugs tenofovir-emtricitabine are taken by individuals with negative HIV serostatus to prevent getting infected by HIV. We study the PrEP coverage needed to reduce the observed HIV prevalence of 5% to a value close to 0%.

    In the fourth and final paper we focus on condom dispositions among MSM. The disposition models from the first paper are extended to better fit an MSM population and are additionally extended to be used for more types of sexual behaviour data.

  • 161.
    Hansson, Disa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Strömdahl, Susanne
    Estimating individual action dispositions using binary and frequency egocentric sexual network dataManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The degree distribution of nodes in a sexual network has been under thorough investigation, as has its implications for the spread of sexually transmitted infections. However, not only the structure of the network is of importance in regulating the propagation of an infection. Two nodes connected by an edge may take actions that reduce the transmission probability through that edge. Condom use is one such action. In this paper, we derive models for individual action dispositions, and how they together generate an outcome on the edge connecting two nodes. We derive two main models, one where two connected nodes generate one outcome together (suitable for casual sex partners), and one where several outcomes is allowed (suitable for steady sex partners). We model different disposition distributions and different rules on how the dispositions generate outcomes, using an egocentric network data set on condom use behaviour.

  • 162.
    Hansson, Disa
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Strömdahl, Susanne
    Leung, KaYin
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Britton, Tom
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Introducing pre-exposure prophylaxis to prevent HIV acquisition among men who have sex with men in Sweden: insights from a mathematical pair-formation modelManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Objectives Since 2017, the Public health Agency of Sweden recommend that pre-exposure prophylaxis for HIV (PrEP) should be offered to high-risk individuals, in particular to men who have sex with men (MSM). The objective of this study is to develop a mathematical model investigating the effect of introducing PrEP to MSM in Sweden.

    Design A pair-formation model, including steady and casual sex partners, is developed to study the impact of introducing PrEP. Two groups are included in the model: sexually high-active MSM and sexually low-active MSM. Three mixing assumptions between the groups are considered.

    Setting A gay-friendly MSM HIV/STI-testing clinic in Stockholm, Sweden. This clinic started offering PrEP to MSM in October 2018.

    Participants The model is calibrated according to detailed sexual behaviour data gathered in 2015 among 403 MSM.

    Results By targeting sexually high-active MSM, a PrEP coverage of 3.5% of the MSM population (10% of all high-actives) would result in the long-term prevalence to drop considerably (close to 0%). While targeting only low-actives would require a PrEP coverage of 35% for a similar reduction. The main effect of PrEP is the reduced susceptibility, whereas the increased HIV-testing rate (every 3rd month) among PrEP users plays a lesser role.

    Conclusions To create a multifaceted picture of the effects of interventions against HIV, we need models that include the different stages of HIV infection and real-world data on detailed sexual behaviour to calibrate the mathematical models. Our findings conclude that targeting HIV high-risk individuals, within HIV risk populations such as MSM, with PrEP programmes could greatly decrease the long-term HIV prevalence in Sweden. Therefore, risk stratification of individuals is of importance in PrEP implementation programmes, to ensure optimising the effect and cost-effectiveness of such programmes.

  • 163.
    Hao, Chengcheng
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Explicit Influence Analysis in Crossover Models2014Doktoravhandling, monografi (Annet vitenskapelig)
    Abstract [en]

    This dissertation develops influence diagnostics for crossover models. Mixed linear models and generalised mixed linear models are utilised to investigate continuous and count data from crossover studies, respectively.

    For both types of models, changes in the maximum likelihood estimates of parameters, particularly in the estimated treatment effect, due to minor perturbations of the observed data, are assessed. The novelty of this dissertation lies in the analytical derivation of influence diagnostics using decompositions of the perturbed mixed models. Consequently, the suggested influence diagnostics, referred to as the delta-beta and variance-ratio influences, provide new findings about how the constructed residuals affect the estimation in terms of different parameters of interest.

    The delta-beta and variance-ratio influence in three different crossover models are studied in Chapters 5-6, respectively. Chapter 5 analyses the influence of subjects in a two-period continuous crossover model. Possible problems with observation-level perturbations in crossover models are discussed. Chapter 6 extends the approach to higher-order crossover models. Furthermore, not only the individual delta-beta and variance-ratio influences of a subject are derived, but also the joint influences of two subjects from different sequences. Chapters 5-6 show that the delta-beta and variance-ratio influences of a particular parameter are decided by the special linear combination of the constructed residuals. In Chapter 7, explicit delta-beta influence on the estimated treatment effect in the two-period count crossover model is derived. The influence is related to the Pearson residuals of the subject. Graphical tools are developed to visualise information of influence concerning crossover models for both continuous and count data. Illustrative examples are provided in each chapter.

  • 164.
    Hao, Chengcheng
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Local Influence Analysis and Cross-over Studies2011Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    With a special reference to cross-over design models with random individual effects, the purpose of this dissertation is to develop new methodology to detect influential observations in the context of mixed linear models with explicit maximum likelihood estimators (MLEs).

    Case-weighted perturbation schemes within and between subjects in mixed models are constructed. It is emphasised that perturbations should be performed under the restriction that explicit MLEs can be obtained in the perturbed model. Two influence functions, the delta-beta influence and variance-ratio influence, are tools to evaluate the influence on the estimates of mean parameters and variance parameters, respectively, with respect to the used perturbations.

    The proposed approach, named the delta-beta-based local influence approach, derives the expressions of the delta-beta and variance-ratio influences for two specific cross-over designs. In both the AB|BA design (2 X 2 cross-over design) and the ABBA|BAAB design, the applied influence functions turn out to have closed-form expressions of residuals from the unperturbed models. Some graphical tools are also presented.

  • 165.
    Hao, Chengcheng
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Liang, Yuli
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Roy, Anuradha
    Equivalency between vertices and centers-coupled-with-radii principal component analyses for interval data2015Inngår i: Statistics and Probability Letters, ISSN 0167-7152, E-ISSN 1879-2103, Vol. 106, s. 113-120Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Centers and vertices principal component analyses are common methods to explain variations within multivariate interval data. We introduce multivariate equicorrelated structures to vertices’ covariance. Assuming the structure, we show equivalence between centers and vertices methods by proving their eigensystems proportional.

  • 166.
    Hao, Chengcheng
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    von Rosen, Dietrich
    von Rosen, Tatjana
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Explicit Influence Analysis in Two-Treatment Balanced Crossover Models2015Inngår i: Mathematical Methods of Statistics, ISSN 1066-5307, E-ISSN 1934-8045, Vol. 24, nr 1, s. 16-36Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper considers how to detect influential observations in crossover models with random individual effects. Two influence measures, the delta-beta influence and variance-ratio influence, are utilized as tools to evaluate the influence of the model on the estimates of mean and variance parameters with respect to case-weighted perturbations, which are introduced to the model for studying the ‘influence’ of cases. The paper provides explicit expressions of the delta-beta and variance-ratio influences for the general two-treatment balanced crossover models when the proposed decompositions for the perturbed models hold. The influence measures for each parameter turn out to be closed-form functions of orthogonal projections of specific residuals in the unperturbed model.

  • 167.
    Hao, Chengcheng
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    von Rosen, Dietrich
    von Rosen, Tatjana
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Influence diagnostics for count data under AB-BA crossover trials2017Inngår i: Statistical Methods in Medical Research, ISSN 0962-2802, E-ISSN 1477-0334, Vol. 26, nr 6, s. 2938-2950Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper aims to develop diagnostic measures to assess the influence of data perturbations on estimates in AB-BA crossover studies with a Poisson distributed response. Generalised mixed linear models with normally distributed random effects are utilised. We show that in this special case, the model can be decomposed into two independent sub-models which allow to derive closed-form expressions to evaluate the changes in the maximum likelihood estimates under several perturbation schemes. The performance of the new influence measures is illustrated by simulation studies and the analysis of a real dataset.

  • 168.
    Hao, Chengcheng
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    von Rosen, Dietrich
    von Rosen, Tatjana
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Local Influence Analysis in AB–BA Crossover Designs2014Inngår i: Scandinavian Journal of Statistics, ISSN 0303-6898, E-ISSN 1467-9469, Vol. 41, nr 4, s. 1153-1166Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this article is to develop methodology for detecting influential observations in crossover models with random individual effects. Various case-weighted perturbations are performed. We obtain the influence of the perturbations on each parameter estimator and on their dispersion matrices. The obtained results exhibit the possibility to obtain closed-form expressions of the influence using the residuals in mixed linear models. Some graphical tools are also presented.

  • 169.
    Hao, Chengcheng
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    von Rosen, Tatjana
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    von Rosen, Dietrich
    Department of Energy and Technology, Swedish University of Agricultural Sciences.
    Influence analysis in two-treatment cross-over designs with special reference to the ABBA|BAAB design2011Rapport (Annet vitenskapelig)
    Abstract [en]

    This work is to develop methodology to detect influential observations in linear mixed model for multiple-period two-treatment cross-over designs. Existence of explicit maximum likelihood estimates (MLEs) of variance parameters as well as of mean parameters in the mixed model with treatment, residual, period and sequence effects is proven. Special reference is taken to the four-period ABBA|BAAB design. Case-weighted perturbations are performed. The influence quantities on each parameter estimate and their dispersion matrix are presented as closed-form functions of residuals in the unperturbed model.

  • 170.
    Hao, Chengcheng
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    von Rosen, Tatjana
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    von Rosen, Dietrich
    Department of Energy and Technology, Swedish University of Agricultural Sciences.
    Local influence analysis in 2 X 2 cross-over designs2011Rapport (Annet vitenskapelig)
    Abstract [en]

    The aim of this work is to develop new methodology to detect influential observations in cross-over design models with random individual effects. Various case-weighted perturbations are performed. We derive the exact solution of influence of the perturbations on each parameter estimate and their dispersion matrix. Closed-form maximum likelihood estimates (MLEs) of variance parameters as well as fixed effect parameters in the cross-over design models are utilised. The work exhibits the possibility to produce closed-form expressions of the influence using the residuals in mixed models. A discussion on restrictions of the case-weighted perturbation schemes is given. Some graphical tools are also presented.

  • 171.
    Hassan, Mahmood Ul
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Hayat, Omar
    Noreen, Zahra
    Selecting the best probability distribution for at-site flood frequency analysis; a study of Torne River2019Inngår i: SN Applied Sciences, ISSN 2523-3963, Vol. 1, nr 12, artikkel-id 1629Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    At-site flood frequency analysis is a direct method of estimation of flood frequency at a particular site. The appropriate selection of probability distribution and a parameter estimation method are important for at-site flood frequency analysis. Generalized extreme value, three-parameter log-normal, generalized logistic, Pearson type-III and Gumbel distributions have been considered to describe the annual maximum steam flow at five gauging sites of Torne River in Sweden. To estimate the parameters of distributions, maximum likelihood estimation and L-moments methods are used. The performance of these distributions is assessed based on goodness-of-fit tests and accuracy measures. At most sites, the best-fitted distributions are with LM estimation method. Finally, the most suitable distribution at each site is used to predict the maximum flood magnitude for different return periods.

  • 172.
    Hedlin, Dan
    University of Southampton.
    A procedure for stratification by an extended Ekman rule2000Inngår i: Journal of Official Statistics, ISSN 0282-423X, E-ISSN 2001-7367, Vol. 16, nr 1, s. 15-29Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper deals with the Ekman rule, which is a well-known method for univariate stratification that approximately minimises the variance of the ordinary expansion estimator. An efficient numerical algorithm for the Ekman rule is presented.

  • 173.
    Hedlin, Dan
    University of Southampton.
    Estimating totals in some U.K. business surveys2002Inngår i: Statistics in Transition, ISSN 1234-7655, Vol. 5, nr 6, s. 943-968Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The paper discusses estimation of the total for some study variables in two business surveys conducted by the U.K. Office for National Statistics. The paper is mainly focused on design-based methods. We ask what the desirable properties of an estimator are and explore several point estimators in a simulation study.

  • 174.
    Hedlin, Dan
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Mitt icke-wallraffande bland undersökningar2017Inngår i: Qvintensen, ISSN 2000-1819, nr 1, s. 9-12Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
  • 175.
    Hedlin, Dan
    Departement of Social statsitics,University of Southampton, the United Kingdom.
    On the Stratification of Highly Skewed Populations (No. 1998:3). R&D Report.1998Rapport (Annet vitenskapelig)
    Abstract [en]

    This paper considers the combined problem of allocation and stratification in order to minimise the variance of the expansion estimator of a total, taking into account that the population is finite. The proof of necessary minimum variance conditions utilises the Kuhn-Tucker Theorem. Stratified simple random sampling with non-negligible sampling fractions is an important design in sample surveys. We go beyond limiting assumptions that have often been used in the past, such as that the stratification equals the study variable or that the sampling fractions are small. We discuss what difference the sampling fractions will make for stratification. In particular, in many surveys the sampling fraction equals one for some strata. The main theorem of this article is applied to a business population.

  • 176.
    Hedlin, Dan
    University of Southampton.
    Score functions to reduce business survey editing at the UK Office for National Statistics2003Inngår i: Journal of Official Statistics, ISSN 0282-423X, E-ISSN 2001-7367, Vol. 19, nr 2, s. 177-199Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A score function associates a number to each item response. The function indicates the relative importance of allocating manual resources to review responses, thereby allowing the survey analyst to prioritise editing efforts. By applying different score functions to the Monthly Inquiry for the Distribution and Services Sector the article discusses how to measure the effectiveness of a score function, and what it is that makes this method effective at reducing manual editing. One finding is that the effectiveness of the technique is rather insensitive to the type of score function. In many situations it is useful to specify a threshold that splits the responses into two groups where manual editing is directed at responses with scores above the threshold. The article suggests a simple graphical tool that allows the analyst to assess the threshold.

  • 177.
    Hedlin, Dan
    Statistiska centralbyrån.
    Small area estimation: a practitioner’s appraisal2008Inngår i: Rivista Internazionale di Scienze Sociali, ISSN 0035-676X, E-ISSN 1827-7918, nr 4, s. 407-417Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Demands of regional statistics combined with pressure to reduce costs and response burden has lead to great interest in Small Area Estimation. Both researchers and practitioners take part in a largely very successful development that still is moving rapidly. However, the National Statistical Institutes in Europe have been rather hesitant to implement SAE, partly because of the different tradition of SAE in terms of statistical inference. NSIs are obliged to as far as possible publish officials statistics that are based on estimators with negligible bias. Fear of model misspecification has been a hindrance to wide application of SAE. Use of a model is now seen as a quality issue. Communication of methods and the resulting quality of statistics is an issue that NSIs have recently given specific attention to.

  • 178.
    Hedlin, Dan
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Using Administrative Data for Statistical Purposes2015Inngår i: The Survey Statistician, nr 71, s. 34-41Artikkel, omtale (Annet vitenskapelig)
  • 179.
    Hedlin, Dan
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Why are design in survey sampling and design of randomised experiments separate areas of statistical science?2015Inngår i: Festschrift in honor of Hans Nyquist on the occasion of his 65th birthday / [ed] Ellinor Fackle-Fornius, Stockholm: Department of Statistics, Stockholm University , 2015, s. 82-95Kapittel i bok, del av antologi (Annet vitenskapelig)
  • 180.
    Hedlin, Dan
    et al.
    Statistiska centralbyrån.
    Chambers, Ray
    van den Brakel, Jan
    Lehtonen, Risto
    Zhang, Li-Chun
    Future challenges of small area estimation2006Inngår i: Statistics in transition, ISSN 1234-7655, Vol. 7, nr 4, s. 759-769Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A panel discussion session entitled as “Future Challenges of Small Area Estimation” was organized in the SAE2005 Conference, with Ray Chambers as the organizer and chair and Jan van den Brakel, Dan Hedlin, Marie Cruddas, Risto Lehtonen, Imbi Traat and Li-Chun Zhang as the discussants. The output of the panel discussion session is summarized in this paper. Each contributor is responsible of the respective piece of text; the paper has been edited by the chairman of the session.

  • 181.
    Hedlin, Dan
    et al.
    Statistiska centralbyrån.
    Dale, Trine
    Haraldsen, Gustav
    Jones, Jaqui
    Developing methods for assessing perceived response burden: a joint report of Statistics Sweden, Statistics Norway and the UK Office for National Statistics2005Rapport (Annet vitenskapelig)
  • 182.
    Hedlin, Dan
    et al.
    University of Southampton.
    Falvey, Hannah
    Quarterly Capital Expenditure Inquiry Review1998Rapport (Annet vitenskapelig)
  • 183.
    Hedlin, Dan
    et al.
    University of Southampton.
    Falvey, Hannah
    Office for National Statistics, U.K..
    Chambers, Ray
    Kokic, Phil
    University of Southampton.
    Does the model matter for GREG estimation?: a business survey example2001Inngår i: Journal of Official Statistics, ISSN 0282-423X, E-ISSN 2001-7367, Vol. 17, nr 4, s. 527-544Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Although asymptotically design-unbiased, GREG estimators may produce bad estimates. The paper examines the behaviour of GREG estimators when the underlying models are misspecified. It shows how an efficient GREG estimator was found for a business survey that posed some problems. The work involved data exploration in several steps, combined with analyses of g-weights, residuals and standard regression diagnostics. We discuss two diagnostics for whether a GREG estimate is reasonable or not. A common justification for the use of GREG estimators is that, being asymptotically design unbiased, they are relatively robust to model choice. However, we show that the property of being asymptotically design unbiased is not a substitute for a careful model specification search, especially when dealing with the highly variable and outlier prone populations that are the focus of many business surveys.

  • 184.
    Hedlin, Dan
    et al.
    Statistiska centralbyrån.
    Fenton, Trevor
    Pont, Mark
    McDonald, John
    Wang, Suojin
    Estimating the undercoverage of a sampling frame due to reporting delays2006Inngår i: Journal of Official Statistics, ISSN 0282-423X, E-ISSN 2001-7367, Vol. 22, nr 1, s. 53-70Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    One of the imperfections of a sampling frame is miscoverage caused by delays in recording real-life events that change the eligibility of population units. For example, new units generally appear on the frame some time after they came into existence and units that have ceased to exist are not removed from the frame immediately. We provide methodology for predicting the undercoverage due to delays in reporting new units. The approach presented here is novel in a business survey context, and is equally applicable to overcoverage due to delays in reporting the closure of units. As a special case, we also predict the number of new-born units per month. The methodology is applied to the principal business register in the UK, maintained by the Office for National Statistics.

  • 185.
    Hedlin, Dan
    et al.
    Statistiska centralbyrån.
    Isaksson, Annica
    Orusild, Tiina
    Svensson, Jörgen
    Urval: från teori till praktik2008Bok (Annet vitenskapelig)
  • 186.
    Hedlin, Dan
    et al.
    Statistiska centralbyrån.
    Lindqvist, Helen
    Erikson, Johan
    Bäckström, Helena
    An experiment on perceived survey response burden among businesses2008Inngår i: Journal of Official Statistics, ISSN 0282-423X, E-ISSN 2001-7367, Vol. 24, nr 2, s. 301-318Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an experiment embedded in a business survey, subsamples were randomized to obtain none, both or either of two motivation-enhancing enclosures that went out with the covering letter: a sheet explaining the purpose of the survey and another sheet informing about feedback of survey results. All businesses obtained a questionnaire on perceptions of the survey. The main conclusion is that perceptions of the usefulness of the survey are improved by the enclosures while there is no evidence of an effect on perceptions of how burdensome the survey is.

  • 187.
    Hedlin, Dan
    et al.
    Statistiska centralbyrån.
    Wang, Suojin
    Texas A&M University, Department of Statistics, College Station, Texas.
    Feeding back information on ineligibility from sample surveys to the frame2004Inngår i: Survey Methodology, ISSN 0714-0045, E-ISSN 1492-0921, Vol. 30, nr 2, s. 167-174Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    It is usually discovered in the data collection phase of a survey that some units in the sample are ineligible even if the frame information has indicated otherwise. For example, in many business surveys a nonnegligible proportion of the sampled units will have ceased trading since the latest update of the frame. This information may be fed back to the frame and used in subsequent surveys, thereby making forthcoming samples more efficient by avoiding sampling nonnegligible units. We investigate what effect on survey estimation the process of feeding back information on ineligibility may have, and derive an expression for the bias that can occur as a result of feeding back. The focus is on estimation of the total using the common expansion estimator. We obtain an estimator that is nearly unbiased in the presence of feed back. This estimator relies on consistent estimates of the number of eligible and ineligible units in the population being available.

  • 188. Hee, Siew Wan
    et al.
    Hamborg, Thomas
    Day, Simon
    Madan, Jason
    Miller, Frank
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Posch, Martin
    Zohar, Sarah
    Stallard, Nigel
    Decision-theoretic designs for small trials and pilot studies: A review2016Inngår i: Statistical Methods in Medical Research, ISSN 0962-2802, E-ISSN 1477-0334, Vol. 25, nr 3, s. 1022-1038Artikkel, forskningsoversikt (Fagfellevurdert)
    Abstract [en]

    Pilot studies and other small clinical trials are often conducted but serve a variety of purposes and there is little consensus on their design. One paradigm that has been suggested for the design of such studies is Bayesian decision theory. In this article, we review the literature with the aim of summarizing current methodological developments in this area. We find that decision-theoretic methods have been applied to the design of small clinical trials in a number of areas. We divide our discussion of published methods into those for trials conducted in a single stage, those for multi-stage trials in which decisions are made through the course of the trial at a number of interim analyses, and those that attempt to design a series of clinical trials or a drug development programme. In all three cases, a number of methods have been proposed, depending on the decision maker’s perspective being considered and the details of utility functions that are used to construct the optimal design.

  • 189. Hogberg, Liselotte
    et al.
    Geli, Patricia
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Ringberg, Hakan
    Melander, Eva
    Lipsitch, Marc
    Ekdahl, Karl
    Age- and serogroup-related differences in observed durations of nasopharyngeal carriage of penicillin-resistant pneumococci2007Inngår i: Journal of Clinical Microbiology, ISSN 0095-1137, E-ISSN 1098-660X, Vol. 45, nr 3, s. 948-952Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Using data from an ongoing Swedish intervention project, the observed durations of nasopharyngeal carriage of penicillin-nonsusceptible Streptococcus pneumoniae (PNSP) (MIC of penicillin G of >= 0.5 mu g/ml) stratified by both pneumococcal serogroup and age of the carrier were compared. The means and 95% confidence intervals (CIs) were estimated by fitting a gamma distribution to the observed duration of carriage for each age and serogroup stratum. The mean observed duration of carriage for all cases was 37 days (95% CI, 35 to 38 days). Children below the age of 5 years carried PNSP for significantly longer periods (43 days; 95% CI, 41 to 45 days) compared with older individuals (25 days; 95% CI, 24 to 27 days). There were also differences within the group of cases below the age of 5 years, as the duration of carriage became significantly shorter for each increasing age step: < 1, 1 to 2, and 3 to 4 years. In addition, patients < 5 years of age carried serogroups 9 and 14 for significantly shorter periods than groups 6 and 23. Serogroup 9 was also carried for significantly shorter periods than group 19. For patients aged 5 years or older, no significant difference in carriage duration for different ages or serogroups could be noted. As young children have the longest duration of PNSP carriage, interventions aiming to reduce the prevalence in this group are of great importance. The results highlight the importance of taking both serogroup and age of the carriers into account when studying the dynamics of pneumococcal transmission in young children.

  • 190.
    Hossain, Md Shakhawat
    et al.
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Ul Hassan, Mahmood
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    Nobi, Mohammad Nur
    Rokonuzzaman, Md
    Stockholms universitet, Samhällsvetenskapliga fakulteten, Statistiska institutionen.
    The impact of stock market development and banks on economic growth for SAARC countries: a panel analysis2012Inngår i: Asian Journal of Research in Business Economics and Management, ISSN 2249-7307, Vol. 2, nr 9, s. 49-60Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The aim of this study is to determine the effect of stock market development and banks on the economic growth in SAARC countries. A random effect panel model is fitted and it fits the data well. It is observed that market capitalization and domestic credit to private sector have significant positive contribution to the economic growth (GDP) for the sampled SAARC countries whereas domestic credit to banking sector has negative contribution.

  • 191.
    Höhle, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    A statistician's perspective on digital epidemiology2017Inngår i: Life Sciences, Society and Policy, ISSN 2195-7819, E-ISSN 2195-7819, Life Sciences, Society and Policy, Vol. 13, artikkel-id 17Artikkel i tidsskrift (Fagfellevurdert)
  • 192.
    Höhle, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Infectious Disease Modelling2016Inngår i: Handbook on Spatial Epidemiology / [ed] A. Lawson, S. Banerjee, R. Haining and L. Ugarte, Chapman & Hall/CRC , 2016Kapittel i bok, del av antologi (Fagfellevurdert)
  • 193.
    Höhle, Michael
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Rank uncertainty: why the “most popular” baby names might not be the most popular2017Inngår i: Significance, ISSN 1740-9705, E-ISSN 1740-9713, Vol. 14, nr 3, s. 30-33Artikkel i tidsskrift (Annet (populærvitenskap, debatt, mm))
    Abstract [en]

    Soon‐to‐be parents, souvenir mug producers and onomatologists are all equally fascinated by baby name statistics. But end‐of‐year lists of the most popular names fail to account for uncertainty says Michael Höhle. Can we trust the rankings?

  • 194.
    Höhle, Michael
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Höhle, Joachim
    Aalborg University.
    Generation and Assessment of Urban Land Cover Maps Using High-Resolution Multispectral Aerial Cameras2013Inngår i: International Journal On Advances in Software, ISSN 1942-2628, E-ISSN 1942-2628, Vol. 6, nr 3-4, s. 272-282Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    New aerial cameras and new advanced geoprocessingtools improve the generation of urban land covermaps. Elevations can be derived from stereo pairs with highdensity, positional accuracy, and efficiency. The combinationof multispectral high-resolution imagery and high-densityelevations enable a unique method for the automaticgeneration of urban land cover maps. In the present paper,imagery of a new medium-format aerial camera and advancedgeoprocessing software are applied to derive normalizeddigital surface models and vegetation maps. These twointermediate products then become input to a tree structuredclassifier, which automatically derives land cover maps in 2Dor 3D. We investigate the thematic accuracy of the producedland cover map by a class-wise stratified design and provide amethod for deriving necessary sample sizes. Correspondingsurvey adjusted accuracy measures and their associatedconfidence intervals are used to adequately reflect uncertaintyin the assessment based on the chosen sample size. Proof ofconcept for the method is given for an urban area inSwitzerland. Here, the produced land cover map with sixclasses (building, wall and carport, road and parking lot, hedgeand bush, grass) has an overall accuracy of 86% (95%confidence interval: 83-88%) and a kappa coefficient of 0.82(95% confidence interval: 0.78-0.85). The classification ofbuildings is correct with 99% and of road and parking lot with95%. To possibly improve the classification further,classification tree learning based on recursive partitioning isinvestigated. We conclude that the open source software “R”provides all the tools needed for performing statistical prudentclassification and accuracy evaluations of urban land covermaps.

  • 195.
    Hössjer, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Asymptotics of LR tests at boundary of parameter space under non-identifiability2007Rapport (Annet (populærvitenskap, debatt, mm))
  • 196.
    Hössjer, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Coalescence theory for a general class of structured populations with fast migration2011Inngår i: Advances in Applied Probability, ISSN 0001-8678, E-ISSN 1475-6064, Vol. 43, nr 4, s. 1027-1047Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In this paper we study a general class of population genetic models where the total population is divided into a number of subpopulations or types. Migration between subpopulations is fast. Extending the results of Nordborg and Krone (2002) and Sagitov and Jagers (2005), we prove, as the total population size N tends to infinity, weak convergence of the joint ancestry of a given sample of haploid individuals in the Skorokhod topology towards Kingman's coalescent with a constant change of time scale c. Our framework includes age-structured models, geographically structured models, and combinations thereof. We also allow each individual to have offspring in several subpopulations, with general dependency structures between the number of offspring of various types. As a byproduct, explicit expressions for the coalescent effective population size N/c are obtained.

  • 197.
    Hössjer, Ola
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Spatial autocorrelations for subdivided populations with invariant migration schemes2012Rapport (Annet vitenskapelig)
  • 198.
    Hössjer, Ola
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Nyberg, Tommy
    Petrovic, Stefan
    Sjöberg, Frank
    Öberg, Tommy
    Bayesian Distributed Detection by Sensor Networks with Missing Data2012Rapport (Annet vitenskapelig)
    Abstract [en]

    We consider detection and identication of a moving target, using a network of sensors. The target emits a signal; a stationary stochastic process corrupted by additive noise, independently across sensors. Before intersensor communication, all sensors reduce external data as energy over disjoint frequency bands and time blocks. One sensor, the internal fusion center (IFC), gathers feature vectors from the other sensors, possibly after message passing. Using Bayesian decision theory, it decides for presence or absence of the target and computes a maximum posterior estimate of target (trajectory and spectral) parameters. The main novelties of the paper are: 1) To apply statistical theory of missing data to an inter-sensor communication protocol which censors weak signals before transmission and an imperfect channel in which some transmitted signals are lost. A Naive Bayes approximate detector is dened, which requires recursive computation of reception probabilities. 2) To derive asymptotic approximations of the distribution of the spectral feature vectors and a Laplace type approximation of the detector. The performance of the proposed Bayesian detector is shown in a simulation study to be only slightly inferior to that of an ideal Bayesian detector (with no missing data), as well as superior to a naive detector.

  • 199.
    Hössjer, Ola
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Ryman, Nils
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för genetik, mikrobiologi och toxikologi.
    Quasi equilibrium, variance effective population size and fixation index for models with spatial structure2012Rapport (Annet vitenskapelig)
  • 200.
    Hössjer, Ola
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Matematiska institutionen.
    Tyvand, Peder A.
    A monoecious and diploid Moran model of random mating2016Inngår i: Journal of Theoretical Biology, ISSN 0022-5193, E-ISSN 1095-8541, Vol. 394, s. 182-196Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    An exact Markov chain is developed for a Moran model of random mating for monoecious diploid individuals with a given probability of self-fertilization. The model captures the dynamics of genetic variation at a biallelic locus. We compare the model with the corresponding diploid Wright-Fisher (WF) model. We also develop a novel diffusion approximation of both models, where the genotype frequency distribution dynamics is described by two partial differential equations, on different time scales. The first equation captures the more slowly varying allele frequencies, and it is the same for the Moran and WF models. The other equation captures departures of the fraction of heterozygous genotypes from a large population equilibrium curve that equals Hardy-Weinberg proportions in the absence of selfing. It is the distribution of a continuous time Ornstein-Uhlenbeck process for the Moran model and a discrete time autoregressive process for the WF model. One application of our results is to capture dynamics of the degree of non-random mating of both models, in terms of the fixation index f(IS). Although f(IS) has a stable fixed point that only depends on the degree of selfing, the normally distributed oscillations around this fixed point are stochastically larger for the Moran than for the WF model.

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