Conservative Sample Size Determination for Repeated Measures Analysis of Covariance.

ABSTRACT: In the design of a randomized clinical trial with one pre and multiple post randomized assessments of the outcome variable, one needs to account for the repeated measures in determining the appropriate sample size. Unfortunately, one seldom has a good estimate of the variance of the outcome measure, let alone the correlations among the measurements over time. We show how sample sizes can be calculated by making conservative assumptions regarding the correlations for a variety of covariance structures. The most conservative choice for the correlation depends on the covariance structure and the number of repeated measures. In the absence of good estimates of the correlations, the sample size is often based on a two-sample t-test, making the 'ultra' conservative and unrealistic assumption tha

SUBMITTER: Morgan TM 

PROVIDER: S-EPMC4100335 | biostudies-literature | 2013 Jul

REPOSITORIES: biostudies-literature