The Solomon four-group method is a type of research method which expands on the traditional pretest-posttest design by including two additional groups to help isolate the effects of treatment and pretesting.
The Solomon four-group design addresses any potential issues with internal validity and external validity which can arise in standard pretest-posttest studies.
The groups of the Solomon four-group method are Group 1, Group 2, Group 3 and Group 4.
Group 1 of the Solomon four-group method receives both the pretest and the treatment/intervention, followed by the posttest.
Group 2 of the Solomon four-group method receives the pretest, but not the treatment/intervention, followed by the posttest, which serves as a control group.
Group 3 of the Solomon four-group method does not receive the pretest, but does receive the treatment/intervention, followed by the posttest.
Group 4 of the Solomon four-group method does not receive the pretest or the treatment/intervention, but is given the posttest, which also serves as a control group.
The design of the Solomon four-group method allows researchers to examine whether the act of taking a pretest influences participants, posttest results and potentially masks the true effect of the treatment.