Solomon four-group design
an experimental design that assesses the effect of having been pretested on the magnitude of the treatment effect. Participants are randomly divided into four groups and each group experiences a different combination of experimental manipulations: the first group (A) receives the pretest, the treatment, and the posttest; the second group (B) receives only the treatment and posttest; the third group (C) receives the pretest, no treatment, and a posttest; and the fourth group (D) receives only a posttest. The major advantages of the Solomon four-group design over a traditional two-group pretest–posttest design are that it reduces the influence of confounds and that it can pinpoint whether changes in the dependent variable are due to some interaction effect between the pretest and the treatment. A major disadvantage, however, is that its analysis and statistics are complex. [Richard L. Solomon]