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  • 1
    In: Biometrics, Wiley, Vol. 72, No. 1 ( 2016-03), p. 253-261
    Abstract: Subject‐specific and marginal models have been developed for the analysis of longitudinal ordinal data. Subject‐specific models often lack a population‐average interpretation of the model parameters due to the conditional formulation of random intercepts and slopes. Marginal models frequently lack an underlying distribution for ordinal data, in particular when generalized estimating equations are applied. To overcome these issues, latent variable models underneath the ordinal outcomes with a multivariate logistic distribution can be applied. In this article, we extend the work of O'Brien and Dunson (2004), who studied the multivariate t ‐distribution with marginal logistic distributions. We use maximum likelihood, instead of a Bayesian approach, and incorporated covariates in the correlation structure, in addition to the mean model. We compared our method with GEE and demonstrated that it performs better than GEE with respect to the fixed effect parameter estimation when the latent variables have an approximately elliptical distribution, and at least as good as GEE for other types of latent variable distributions.
    Type of Medium: Online Resource
    ISSN: 0006-341X , 1541-0420
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2016
    detail.hit.zdb_id: 2054197-1
    SSG: 12
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  • 2
    Online Resource
    Online Resource
    Wiley ; 2015
    In:  Biometrics Vol. 71, No. 2 ( 2015-06), p. 548-555
    In: Biometrics, Wiley, Vol. 71, No. 2 ( 2015-06), p. 548-555
    Abstract: This work is motivated by a meta‐analysis case study on antipsychotic medications. The Michaelis–Menten curve is employed to model the nonlinear relationship between the dose and receptor occupancy across multiple studies. An intraclass correlation coefficient (ICC) is used to quantify the heterogeneity across studies. To interpret the size of heterogeneity, an accurate estimate of ICC and its confidence interval is required. The goal is to apply a recently proposed generic beta‐approach for construction the confidence intervals on ICCs for linear mixed effects models to nonlinear mixed effects models using four estimation methods. These estimation methods are the maximum likelihood, second‐order generalized estimating equations and two two‐step procedures. The beta‐approach is compared with a large sample normal approximation (delta method) and bootstrapping. The confidence intervals based on the delta method and the nonparametric percentile bootstrap with various resampling strategies failed in our settings. The beta‐approach demonstrates good coverages with both two‐step estimation methods and consequently, it is recommended for the computation of confidence interval for ICCs in nonlinear mixed effects models for small studies.
    Type of Medium: Online Resource
    ISSN: 0006-341X , 1541-0420
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2015
    detail.hit.zdb_id: 2054197-1
    SSG: 12
    Location Call Number Limitation Availability
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  • 3
    In: Biometrical Journal, Wiley, Vol. 62, No. 1 ( 2020-01), p. 34-52
    Abstract: Combining data from different studies has a long tradition within the scientific community. It requires that the same information is collected from each study to be able to pool individual data. When studies have implemented different methods or used different instruments (e.g., questionnaires) for measuring the same characteristics or constructs, the observed variables need to be harmonized in some way to obtain equivalent content information across studies. This paper formulates the main concepts for harmonizing test scores from different observational studies in terms of latent variable models. The concepts are formulated in terms of calibration, invariance, and exchangeability. Although similar ideas are present in measurement reliability and test equating, harmonization is different from measurement invariance and generalizes test equating. In addition, if a test score needs to be transformed to another test score, harmonization of variables is only possible under specific conditions. Observed test scores that connect all of the different studies, are necessary to be able to test the underlying assumptions of harmonization. The concepts of harmonization are illustrated on multiple memory test scores from three different Canadian studies.
    Type of Medium: Online Resource
    ISSN: 0323-3847 , 1521-4036
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2020
    detail.hit.zdb_id: 131640-0
    detail.hit.zdb_id: 1479920-0
    SSG: 12
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  • 4
    Online Resource
    Online Resource
    Wiley ; 2022
    In:  Biometrical Journal Vol. 64, No. 7 ( 2022-10), p. 1340-1360
    In: Biometrical Journal, Wiley, Vol. 64, No. 7 ( 2022-10), p. 1340-1360
    Abstract: The DerSimonian–Laird (DL) weighted average method for aggregated data meta‐analysis has been widely used for the estimation of overall effect sizes. It is criticized for its underestimation of the standard error of the overall effect size in the presence of heterogeneous effect sizes. Due to this negative property, many alternative estimation approaches have been proposed in the literature. One of the earliest alternative approaches was developed by Hardy and Thompson (HT), who implemented a profile likelihood instead of the moment‐based approach of DL. Others have further extended this likelihood approach and proposed higher‐order likelihood inferences (e.g., Bartlett‐type corrections). In addition, corrections factors for the estimated DL standard error, like the Hartung–Knapp–Sidik–Jonkman (HKSJ) adjustment, and the restricted maximum likelihood (REML) estimation have been suggested too. Although these improvements address the uncertainty in estimating the between‐study variance better than the DL method, they all assume that the true within‐study standard errors are known and equal to the observed standard errors of the effect sizes. Here, we will treat the observed standard errors as estimators for the within‐study variability and we propose a bivariate likelihood approach that jointly estimates the overall effect size, the between‐study variance, and the potentially heteroskedastic within‐study variances. We study the performance of the proposed method by means of simulation, and compare it to DL (with and without HKSJ), HT, their higher‐order likelihood methods, and REML. Our proposed approach seems to have better or similar coverages compared to the other approaches and it appears to be less biased in the case of heteroskedastic within‐study variances when this heteroskedasticty is correlated with the effect size.
    Type of Medium: Online Resource
    ISSN: 0323-3847 , 1521-4036
    URL: Issue
    RVK:
    Language: English
    Publisher: Wiley
    Publication Date: 2022
    detail.hit.zdb_id: 131640-0
    detail.hit.zdb_id: 1479920-0
    SSG: 12
    Location Call Number Limitation Availability
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