June 19, 2024

In psychotherapy research, a waitlist control group is a group of participants who do not receive the experimental treatment, but who are put on a waiting list to receive the intervention after the active treatment group does.

The waitlist 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.

At a Glance

In an experiment, some people may be randomly selected for the waitlist group. They also closely resemble the participants in the experimental group (or the individuals who receive the treatment).

While participants in this group do not immediately receive the treatment, they do eventually. A waitlist control group is often used in situations where researchers want to look at an untreated comparison group, but it would be unethical to deny those individuals access to the treatment.

Why a Waitlist Control Group Is Important

A waitlist 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 waitlist control group serves as a benchmark, allowing researchers to compare the experimental group to the waitlist 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 waitlist 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.

Prevalence

The use of waitlists in psychotherapy research is common. According to one study, around 73% of published psychological treatment studies rely on waitlist controls.

Uses for a Waitlist Control Group

Many types of psychological and behavioral health research use waitlist control groups. It is used in studying the effect of interventions on:

  • Alcohol consumption
  • Depression
  • Anxiety
  • Promoting healthy behaviors, such as stress management

Shortcomings of a Waitlist Control Group

While using waitlist 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 waitlist control group may artificially inflate estimates of the intervention effect. In this particular study, researchers looked at the effect of an intervention on problem drinking.

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.

However, the researchers note that this bias can vary depending on the study population. Due to this potential bias, researchers recommend that waitlist control groups should only be used if this threat has been carefully evaluated.

A 2022 research summary also suggested that the use of waitlist control groups may suggest that a treatment is more effective than it actually is. For example, meta-analyses have shown that the effect sizes for anxiety treatment studies that use waitlist controls are much higher than studies that use placebo controls.

In some cases, the condition of patients on the waitlist may decline when treatment is delayed. When they do finally receive treatment, it can make the intervention appear more effective than it would normally appear, since getting any kind of treatment may lead to improvements.

Reducing Wait Times for the Control Group

Since waiting times might impact results, some researchers have suggested that wait times should be adjusted based on how long treatment takes for the experimental group. This can help make the timing more similar for both groups and allow people in the waitlist control group to begin their treatment earlier. 

The advantage of this approach would be that it would make the research process more efficient and reduce the number of people who drop out of the study before receiving treatment.

Takeaway

If you are participating in psychology research, you might be assigned to a waitlist control group. Such groups allow participants to access an intervention, although treatment might be delayed. Such research helps researchers compare the results of intervention to a control group while still ensuring that people eventually access treatments that may help.

Waitlist control groups can be useful, but they can also have some downsides. Wait times may have an impact on intervention effects. That’s why it is important for researchers to be aware of these potential biases and look for ways to help reduce wait times as much as possible.

Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. American Psychological Association Dictionary of Psychology. APA Dictionary of Psychology: wait-list control group.

  2. Kinser PA, Robins JL. Control group design: Enhancing rigor in research of mind-body therapies for depression.  Evidence-Based Complementary and Alternative Medicine. 2013;2013:1-10. doi:10.1155/2013/140467

  3. Patterson B, Boyle MH, Kivlenieks M, Van Ameringen M. The use of waitlists as control conditions in anxiety disorders research. Journal of Psychiatric Research. 2016;83:112-120. doi:10.1016/j.jpsychires.2016.08.015

  4. McCauley JL, Killeen T, Gros DF, Brady KT, Back SE. Posttraumatic stress disorder and co-occurring substance use disorders: Advances in assessment and treatment. Clin Psychol (New York). 2012;19(3). doi:10.1111/cpsp.1200

  5. Cunningham JA, Kypri K, McCambridge J. Exploratory randomized controlled trial evaluating the impact of a waiting list control design. BMC Med Res Methodol. 2013;13(1):150. doi:10.1186/1471-2288-13-150

  6. Faltinsen E, Todorovac A, Staxen Bruun L, et al. Control interventions in randomised trials among people with mental health disorders. Cochrane Methodology Review Group, ed. Cochrane Database of Systematic Reviews. 2022;2022(4). doi:10.1002/14651858.MR000050.pub2

By Nancy Schimelpfening

Nancy Schimelpfening, MS is the administrator for the non-profit depression support group Depression Sanctuary. Nancy has a lifetime of experience with depression, experiencing firsthand how devastating this illness can be.  

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