The Solomon four-group design is a research method developed by Richard Solomon in 1949. 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. The four groups have four different experiences: 1. * Pre-test, treatment, post-test 2. * Pre-test, no treatment, post-test 3. * Treatment, post-test 4. * No treatment, post-test The effectiveness of the treatment can be evaluated by comparisons between groups 1 and 3 and between groups 2 and 4.