Solomon four-group design

The Solomon four-group design is a research method developed by Richard Solomon in 1949.^[1] It is sometimes used in social science, psychology and medicine. It can be used if there are concerns that the treatment might be sensitized by the pre-test.^[2] In addition of the usual two groups (treatment and control), it has a second pair of groups who do not receive a pre-intervention evaluation.

Structure

The structure of the trial is shown in the table :^{[citation needed]}

The four groups in the Solomon design

Group	Pre-intervention	Intervention	Post-intervention
1	Test	Treatment	Test
2	Test	Control	Test
3	No test	Treatment	Test
4	No test	Control	Test

The first two groups receive the evaluation test before and after the study, as in a normal two-group trial. The second groups receive the evaluation only after the study.^{[citation needed]}

The effectiveness of the treatment can be evaluated by comparisons between groups 1 and 3 and between groups 2 and 4.^{[citation needed]}. In addition, the effect of the pre-treatment evaluation can be calculated by comparing the control group who received the pre-treatment evaluation with those who did not (groups 2 and 4).

Various statistical treatments for the Solomon four-group design have been put forward, including Stouffer's Z and Monte Carlo.^[3][4]