SAS/STAT Software

SEQTEST Procedure

The purpose of the SEQTEST procedure is to perform interim analyses for group sequential clinical trials. A group sequential trial provides for interim analyses before the formal completion of the trial while maintaining the specified overall Type I and Type II error probability levels.

Features of the SEQTEST Procedure

At each stage, the data are analyzed with a statistical procedure such as the REG procedure, and a test statistic and its associated information level are computed. The information level is the amount of information available about the unknown parameter. For a maximum likelihood statistic, the information level is the inverse of its variance.

You then use the SEQTEST procedure to compare the test statistic with the corresponding boundary values obtained with the SEQDESIGN procedure.

If the information levels do not match the information levels specified in the design, the SEQTEST procedure modifies the boundary values to adjust for new information levels.

At the end of a trial, the parameter estimate is computed. The median unbiased estimate, confidence limits, and p-value depend on the specified sample space ordering. A sample space ordering specifies the ordering for test statistics resulting in the stopping of a trial. That is, for all the statistics in the rejection region and in acceptance region, the SEQTEST procedure provides three different sample space orderings: the stage-wise ordering uses counterclockwise ordering around the continuous region, the LR ordering uses the distance between the observed Z statistic, z, and its hypothetical value, and the MLE ordering uses the observed maximum likelihood estimate.

Note that for some clinical trials, the information levels are derived from statistics based on individuals specified in the design plan and might not reach the target information levels. Thus, instead of specifying the number of individuals in the protocol, the information levels can be specified. You can then adjust the sample sizes to achieve the information levels for the trial.

Output from the SEQTEST Procedure

In addition to the boundary values and test statistics for the group sequential trial, the SEQTEST procedure also computes the following quantities:
  • average sample sizes (as a percentage of the corresponding fixed-sample size) 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
  • conditional power given the most recently observed statistic under specified hypothetical references
  • predictive power given the most recently observed statistic
  • repeated confidence intervals for the parameter from the observed statistic at each stage
  • parameter estimate, p-value for hypothesis testing, and median and confidence limits for the parameter at the conclusion of a sequential trial

For further details see the SAS/STAT User's Guide: The SEQTEST Procedure
( PDF | HTML )