In experimental designs with nested structures, entire groups (such as schools) are often assigned to treatment conditions. Key aspects of the design in these cluster-randomized experiments involve knowledge of the intraclass correlation structure, the effect size, and the sample sizes necessary to achieve adequate power to detect the treatment effect. However, the units at each level of the hi...

One of the most common requests that statisticians get from investigators are sample size calculations or sample size justifications. The sample size is the number of patients or other experimental units included in a study, and determining the sample size required to answer the research question is one of the first steps in designing a study. Although most statistical textbooks describe techni...

We develop a comprehensive and large-sample measure of a firm’s information quality. The measure is the ratio of firm-specific return variation to firm-specific cash-flow variation. Empirical evidence supports the validity of our measure. Using this measure, we find that cost of equity capital decreases by about -0.4% on an annual basis if a firm’s information quality increases by one standard ...

We reviewed all 717 manuscripts published in the 1997 issues of the British and American volumes of the Journal of Bone and Joint Surgery and in Clinical Orthopaedics and Related Research, from which 33 randomised, controlled trials were identified. The results and sample sizes were used to calculate the statistical power of the study to distinguish small (0.2 of standard deviation), medium (0....

Regulatory authorities require that the sample size of a confirmatory trial is calculated prior to the start of the trial. However, the sample size quite often depends on parameters that might not be known in advance of the study. Misspecification of these parameters can lead to under- or overestimation of the sample size. Both situations are unfavourable as the first one decreases the power an...

BACKGROUND Empathy plays an important role in healthy dentist and patient relationship. Hence, the aim of the study is to (a) to measure the self-reported empathy levels among dental undergraduate and postgraduate students. (b) To review the trend of changes in empathy level with experience, age, and gender among dental undergraduate and postgraduate students. MATERIALS AND METHODS This cross...

Sample size justification is an important consideration when planning a clinical trial, not only for the main trial but also for any preliminary pilot trial. When the outcome is a continuous variable, the sample size calculation requires an accurate estimate of the standard deviation of the outcome measure. A pilot trial can be used to get an estimate of the standard deviation, which could then...

BACKGROUND Usually the researchers performing meta-analysis of continuous outcomes from clinical trials need their mean value and the variance (or standard deviation) in order to pool data. However, sometimes the published reports of clinical trials only report the median, range and the size of the trial. METHODS In this article we use simple and elementary inequalities and approximations in ...