In addition to computing the boundary values for a group sequential design, the SEQDESIGN procedure computes the following quantities:
maximum sample size (as a percentage of the corresponding fixed-sample size) if the trial does not stop at an interim stage
average sample numbers (as percentages of the corresponding fixed-sample sizes for nonsurvival data or fixed-sample numbers of events for survival data) under various hypothetical references, including the null and alternative references
stopping probabilities at each stage under various hypothetical references to indicate how likely it is that the trial will stop at that stage
If you specify a SAMPLESIZE statement, the SEQDESIGN procedure also computes the following quantities:
sample sizes that are required at each stage for the specified hypothesis test for nonsurvival data, in both fractional and integer numbers
the number of events, time, and sample size that are required at each stage for the specified hypothesis test for survival data, in both fractional and integer-valued times or in both fractional and integer-valued sample sizes
Furthermore, the CEILADJDESIGN=INCLUDE option in the SAMPLESIZE statement creates an additional group sequential design that corresponds to the integer-valued sample sizes at the stages for the nonsurvival data, and to the integer-valued times or sample sizes at the stages for the survival data. When CEILADJDESIGN=INCLUDE, the SEQDESIGN procedure also displays the ceiling-adjusted design information in the "Design Information" table and the ceiling-adjusted design boundary information in the new "Ceiling-Adjusted Design Boundary Information" table.
You can create more than one design by specifying multiple DESIGN statements, and then you can choose the design that has the most desirable features. The next two subsections introduce some basic aspects of group sequential designs that are useful for getting started with the SEQDESIGN procedure.