The wait list control group serves two purposes. First, it provides an untreated comparison for the active experimental group to determine if the treatment had an effect. By serving as a comparison group, researchers are able to isolate the independent variable and look at the impact it had. Second, it allows the wait-listed participants an opportunity to obtain the intervention at a later date.
Importance
A wait list control group is often thought to be preferable to a no-treatment control group in cases where it would be unethical to deny participants access to treatment. The wait list control group serves as a benchmark, allowing researchers to compare the experimental group to the wait list control group to see what sort of impact changes to the independent variable produced. It essentially allows researchers to assess the effect of the intervention against not receiving treatment during that same time period (while still providing all participants with treatment eventually). Because participants have been randomly assigned to either the wait list control group or the experimental group, it can be assumed that the groups are comparable. Any differences between the two groups are therefore the result of the manipulations of the independent variable. The experimenters carry out the exact same procedures with both groups with the exception of the manipulation of the independent variable in the experimental group.
Types of Research
Many types of psychological and behavioral health research use wait list control groups. It is used in studying the effect of interventions on alcohol consumption, depression and anxiety, and promoting healthy behaviors, such as stress management.
Shortcomings
While using wait list control groups has been seen as an ethical alternative to having a control group, it can pose problems. A 2013 study in BMC Medical Research Methodology suggested that using a wait list control group may artificially inflate estimates of the intervention effect. The idea is that by telling people to wait for treatment, they are stalled in the stage of change related to readiness and do not move forward to action on their own. So rather than attempting behavior change on their own, or seeking other avenues of help, they wait, possibly showing less improvement than a simple control group would show. In this particular study, researchers looked at the effect of an intervention on problem drinking.
