The GLMPOWER Procedure

Sample Size Adjustment Options

By default, PROC GLMPOWER rounds sample sizes conservatively (down in the input, up in the output) so that all total sizes and sample sizes for individual design profiles are integers. This is generally considered conservative because it selects the closest realistic design providing at most the power of the (possibly fractional) input or mathematically optimized design. In addition, all design profile sizes are adjusted to be multiples of their corresponding weights. If a design profile is present more than once in the exemplary data set, then the weights for that design profile are summed. For example, if a particular design profile is present twice in the exemplary data set with weight values 2 and 6, then all sample sizes for this design profile become multiples of $2 + 6 = 8$.

With the NFRACTIONAL option, sample size input is not rounded, and sample size output is reported in two versions, a raw fractional version and a ceiling version rounded up to the nearest integer.

Whenever an input sample size is adjusted, both the original (nominal) and adjusted (actual) sample sizes are reported. Whenever computed output sample sizes are adjusted, both the original input (nominal) power and the achieved (actual) power at the adjusted sample size are reported.