BACKGROUND Statistical models based on item response theory were used to examine (a) the performance of individual Positive and Negative Syndrome Scale (PANSS) items and their options, (b) the effectiveness of various subscales to discriminate among individual differences in symptom severity, and (c) the appropriateness of cutoff scores recently recommended by Andreasen and her colleagues (2005...

BACKGROUND Patient-reported outcomes (PRO) that comprise all self-reported measures by the patient are important as endpoint in clinical trials and epidemiological studies. Models from the Item Response Theory (IRT) are increasingly used to analyze these particular outcomes that bring into play a latent variable as these outcomes cannot be directly observed. Preliminary developments have been p...

For testing both one-sided and two-sided hypotheses concerning several treatment arms in group sequentially performed clinical trials with arbitrary outcome variables, a general method is considered that allows one to completely self-design a study. All information available prior to a stage is used for estimating the sample size and the weight for the next step. In "using up" the variance, the...

This paper develops an empirical likelihood approach to testing for the presence of uniform stochastic ordering (or hazard rate ordering) among univariate distributions based on independent random samples from each distribution. The proposed test statistic is formed by integrating a localized empirical likelihood statistic with respect to the empirical distribution of the pooled sample. The asy...

This paper proposes a marginalized model for repeated or otherwise hierarchical, overdispersed time-to-event outcomes, adapting the so-called combined model for time-to-event outcomes of Molenberghs et al (2012), who combined gamma and normal random effects. The two sets of random effects are used to accommodate simultaneously correlation between repeated measures and overdispersion. The propos...

OBJECTIVES To examine the strengths and weaknesses of the national and local schemes for preregistration house officers to spend four months in general practice, to identify any added value from such placements, and to examine the impact on career choices. DESIGN Review of all studies that reported on placements of preregistration house officers in general practice. SETTING 19 accounts of p...

BACKGROUND Simon's two-stage design is the most widely implemented among multi-stage designs in phase II clinical trials to assess the activity of a new treatment in a single-arm study. In this two-stage design, the sample size from the second stage is fixed regardless of the number of responses observed in the first stage. METHODS We develop a new minimax adaptive design for phase II clinica...

SUMMARY There is an immediate need for tools to both analyse and visualize in real-time single-nucleotide polymorphisms, insertions and deletions, and other structural variants from new sequence file formats. We have developed VarB software that can be used to visualize variant call format files in real time, as well as identify regions under balancing selection and informative markers to diffe...

A common objective of biomarker studies is to develop a predictor of patient survival outcome. Determining the number of samples required to train a predictor from survival data is important for designing such studies. Existing sample size methods for training studies use parametric models for the high-dimensional data and cannot handle a right-censored dependent variable. We present a new trai...

We compare test construction using CTT and IRT in several sample sizes (from N=20 to N=5000) and degrees of representativeness (represented by selecting the top 20%, 40%, 60%, 80% or 100% of a population) using a Monte-Carlo simulation design. Little support was found for our hypothesis that IRT would outperform CTT in building informative tests, especially in large or unrepresentative samples....