The importance of power and sample size estimation for study design and analysis.

A population average regression model is proposed to assess the marginal effects of covariates on the cumulative incidence function when there is dependence across individuals within a cluster in the competing risks setting. This method extends the Fine-Gray proportional hazards model for the subdistribution to situations, where individuals within a cluster may be correlated due to unobserved s...

Some quality control schemes have been developed when several related quality characteristics are to be monitored. The familiar multivariate process monitoring and control procedure is the Hotelling’s T 2 control chart for monitoring the mean vector of the process. It is a direct analog of the univariate shewhart x̄ chart. As in the case of univariate, the ARL improvements are very important par...

BACKGROUND Systematic review and meta-analysis currently underpin much of evidence-based medicine. Such methodologies bring order to previous research, but future research planning remains relatively incoherent and inefficient. METHODS To outline a framework for evaluation of health interventions, aimed at increasing coherence and efficiency through i) making better use of information contain...

The importance of assessing fidelity has been emphasized recently with increasingly sophisticated definitions, assessment procedures, and integration of fidelity data into analyses of outcomes. Fidelity is often measured through observation and coding of instructional sessions either live or by video. However, little guidance has been provided about how to determine the number of observations n...

The use of effect size estimates in planning the sample size necessary for a future study can introduce substantial bias in the sample size planning process. For instance, the uncertainty associated with the effect size estimate may result in average statistical power that is substantially lower than the nominal power specified in the calculation. The present manuscript examines methods for inc...

Attention-Deficit Hyperactive Disorder (ADHD) is one of the most common mental health disorders amongst school-aged children with an estimated prevalence of 5% in the global population (American Psychiatric Association, 2013). Stimulants, particularly methylphenidate (MPH), are the first-line option in the treatment of ADHD (Reeves and Schweitzer, 2004; Dopheide and Pliszka, 2009) and are presc...