Group Randomization
Ref: Grizzle, J. and Feng, Ziding, Personal Communication
This program performs power calculations for studies in which the group is the unit of randomization. The groups are assumed to be the same size. A within-group correlation between individuals must be specified by the user. A t-test is used to test the mean response. Responses can be continuous (normal) or binary (binomial); in either case the sample mean over all groups is assumed normal.
The groups can be unmatched or pair-matched. For pair-matched studies the user must specify a within-pair correlation between sample means. The study design can be pre-post (before and after intervention) or post-only. For pre-post studies the user must specify an autocorrelation between pre and post sample means. Pre-post studies can be cross-sectional or cohort, the only difference being that the user should specify a larger autocorrelation for cohort studies.
Power calculations are performed using a function of the group means, treating it as an individual measure and assuming an appropriate form of the t-test will be used in the analysis.
This option computes the variance of the function of group means that arises from the study design (cohort, pre-post, matched, etc.).
The variance will be a function of:
Pair-matched studies usually involve computing a difference within matched pairs which represents a "treatment effect." The test usually is that this difference is equal to zero and gives rise to a one-sample t-test. Unmatched studies give rise to a two-sample t-test.
The program can compute any one of the following:
when the user supplies values for the other four.