Statistical treatment of the Solomon four-group design: A meta-analytic approach.

Abstract

One of the causes of the underuse of the Solomon four-group design may be that the complete details for the statistical analysis have not previously been presented. The primary issue previously unaddressed was how to combine an analysis of the effect of the treatment in the posttest-only groups with the same effect in the pre- and posttest groups (after an earlier phase of the analysis has shown no evidence of pretest sensitization.) A meta-analytic solution for this problem is proposed, and the entire analysis is presented, complete with flowchart and example. It is shown that the analysis has adequate statistical power even if the total N is not increased from that of a posttest-only design, removing the last of the serious objections to the Solomon design.