To address the challenges to the internal and external validity of pretest-posttest designs, psychologist Richard Solomon created a four-group design in 1949, consisting of two control groups and two treatment or experimental groups. Each group consisted of four individuals.
The purpose of this design is to allow researchers to compare those who have received treatment to those who have not, while controlling for possible bias caused by knowing that you have been assigned to either a treatment or a control group.
It is important to note that although a Solomon four-group design is considered a controlled experiment, it is not an unbiased one. The reason is that you cannot assign people to different groups without also assigning them to different treatments or interventions. This fact makes the results of studies using this design difficult to interpret because we can't be sure if the differences observed between the groups are due to the intervention or simply due to chance.
Studies using the Solomon four-group design usually involve multiple measurements over time on each participant. These can be self-reported questions asked through surveys or interviews, or they may include physiological measures such as blood tests or brain scans. The goal is to see how participants' responses change over time in response to different interventions.
Some studies may include more than four groups.
The Solomon four-group design is a research method that aims to account for the effect of pretesting on later posttest results. Researchers use a pretest-posttest paradigm to demonstrate that treatment exposure resulted in variations in pretest and posttest scores. The four-group design allows researchers to compare the effects of different treatments or interventions with no additional risk to subjects. For example, one group may receive standard care while another receives an intervention such as a clinical trial subject to entry criteria. A third group may be given a placebo; a fourth group can serve as a control and not receive any treatment or intervention.
In addition to comparing different methods of treatment or intervention, researchers can also use this method to study how subjects respond to a single method over time (i.e., intra-subject comparisons). For example, someone who experiences pain from arthritis may have their level of pain assessed before and after a course of treatment. The researcher could then compare the individual's pre- and posttreatment scores to see which method was more effective at reducing pain.
Finally, the Solomon four-group design can be used when trying to determine how much of an effect one specific variable had on another.
The Solomon four-group design is an experimental design that evaluates the plausibility of pretest sensitization effects, or if taking a pretest changes results on successive administrations of the test. The design was proposed by John B. Solomon in 1978.
It is so named after its inventor, who called it this because it has four factors and allows one to investigate the effect of each group member. The four factors are: (1) the order in which groups receive different doses of the antigen (2) the number of injections given (3) the interval between injections, and (4) the time allowed for the immune response following injection. This design is useful when trying to distinguish between the effects of these various factors on the antibody response.
In this type of study, animals are divided into four equal groups. Each animal receives an initial dose of the antigen, followed by three subsequent doses at intervals of about two weeks. The order in which the groups receive the doses of the antigen is important because it can affect how people respond to vaccines; researchers want to know if previous exposure to a vaccine component affects people's responses to later exposures. For example, people may become "sensitized" to a protein in a vaccine after they have been exposed to it previously. This would show up as lower levels of antibodies against that protein if it were injected again later.