Why Do EMDR Researchers Use Control Groups?

Researchers use control groups in Eye Movement Desensitization and Reprocessing (EMDR) studies to understand whether improvements in symptoms are related to EMDR therapy rather than other factors. By comparing people receiving EMDR with those receiving another treatment, usual care, or delayed treatment, researchers can better evaluate how effective EMDR is.

Control groups are an important part of clinical research because people may experience changes in symptoms for several reasons. A comparison group helps researchers determine whether EMDR produces benefits beyond those changes.

What Is a Control Group in EMDR Research?

A control group is a group of participants whose experiences or outcomes are compared with those of people receiving the treatment being studied.

In EMDR research, participants may be divided into two groups:

• EMDR treatment group: Participants receive EMDR therapy during the study.

• Control group: Participants receive a different treatment, continue with their usual care, or wait to begin treatment.

Researchers then measure symptoms in both groups to see how their outcomes compare.

For example, a study investigating EMDR for Post-Traumatic Stress Disorder (PTSD) might measure participants' symptoms before and after treatment. If the EMDR group experiences greater symptom improvement than the control group, this provides evidence that EMDR may have contributed to the difference.

However, the strength of that conclusion depends on how the study was designed and conducted.

Why Are Control Groups Important in EMDR Studies?

Control groups help researchers distinguish the effects of EMDR from improvements that might occur for other reasons.

People's symptoms can change over time, even without receiving the specific treatment being investigated. Some participants may also benefit from additional support, changes in their circumstances, or other care they receive during a study.

Without a comparison group, researchers cannot easily determine how much of the reported improvement is attributable to EMDR itself.

Control groups help researchers answer several important questions:

• Do participants receiving EMDR improve more than those who have not yet received treatment?

• Does EMDR produce outcomes similar to those of other established therapies?

• Are improvements maintained when researchers measure symptoms later?

• How much of the improvement may be associated with factors other than the specific treatment being studied?

These comparisons help researchers develop a clearer understanding of EMDR's effectiveness.

What Types of Control Groups Are Used in EMDR Research?

Different control groups help answer different research questions. Three common approaches are waiting-list controls, usual-care controls, and active-treatment comparisons.

1. Waiting-List Control Groups

Participants assigned to a waiting-list control group do not receive the study treatment immediately. They may be offered EMDR after the comparison period ends.

Researchers compare their symptoms with those of participants who received EMDR during that period.

This design helps determine whether people receiving EMDR experience greater improvement than people who have not yet begun the treatment.

However, waiting-list comparisons have limitations. Participants who know they are waiting for treatment may have different expectations or experiences from those actively receiving therapy.

A positive result against a waiting-list group therefore does not automatically mean EMDR is more effective than another established treatment.

2. Usual-Care Control Groups

In a usual-care control group, participants continue receiving the care ordinarily available to them.

Depending on the study, this might include routine mental health appointments, medication management, supportive services, or other existing treatment.

Researchers compare outcomes between participants receiving EMDR and those receiving usual care.

Because usual care can differ across healthcare settings and studies, understanding exactly what the comparison group received is important when interpreting the findings.

3. Active-Treatment Comparison Groups

Some EMDR studies compare EMDR directly with another psychological treatment.

For example, researchers may compare EMDR with trauma-focused Cognitive Behavioral Therapy (CBT), which helps people address distressing thoughts and responses associated with traumatic experiences.

These studies help answer a different question from waiting-list research: How does EMDR compare with another treatment that is already being used?

Both treatment groups may improve substantially. Researchers then examine whether there are meaningful differences in symptom reduction, treatment completion, or longer-term outcomes.

A finding that one treatment is not statistically different from another does not necessarily establish that the two treatments are equally effective. That conclusion requires appropriate study design and sufficient evidence.

How Do Researchers Assign Participants to Control Groups?

Many clinical studies use a method called random assignment.

In a randomized controlled trial (RCT), participants are assigned to study groups by chance rather than by personal preference or a researcher's decision.

Random assignment helps reduce the possibility that one group begins the study with characteristics that could influence the results.

For example, researchers want to avoid having one group composed mainly of participants with milder PTSD symptoms while another group includes people with more persistent symptoms.

Random assignment helps make the groups more comparable, although differences can still occur, especially in smaller studies.

Researchers then examine whether the groups experience different outcomes over the course of the study.

Not every EMDR study uses random assignment, but randomized controlled trials are particularly valuable when investigating whether a treatment causes improvement.

What Have Control-Group Studies Found About EMDR?

Research comparing EMDR with waiting-list groups, usual care, and other psychological treatments has contributed substantially to the evidence supporting EMDR for PTSD.

A 2013 Cochrane systematic review of psychological therapies for PTSD examined 70 studies involving 4,761 participants across multiple psychological treatments.

The review found that EMDR was associated with greater reductions in clinician-rated PTSD symptoms than waiting-list or usual-care conditions. It also found no statistically significant differences immediately after treatment between EMDR and certain other established psychological therapies, including trauma-focused cognitive behavioral therapy.

However, the authors identified methodological limitations and rated the certainty of evidence for the comparisons as very low.

A more recent systematic review, published in the Journal of Affective Disorders in January 2026, specifically examined EMDR compared with waiting-list controls.

The researchers reviewed 12 randomized controlled trials involving 690 participants. They found that EMDR may reduce PTSD symptoms more than waiting-list conditions, but rated the certainty of evidence as low to very low because of limitations in the included studies.

The review also noted uncertainty about longer-term outcomes.

These findings illustrate why control groups matter. They allow researchers to evaluate differences in outcomes while also examining how confidently those differences can be attributed to treatment.

Do All EMDR Studies Need Control Groups?

Not every EMDR study requires a control group.

Different research designs serve different purposes. Some studies examine participants' experiences, treatment satisfaction, symptom changes, or the practical delivery of EMDR.

For example, an observational study may collect information from people who have already used EMDR and ask whether they noticed improvements in their symptoms.

This type of research can provide useful information about people's experiences and areas for further investigation.

However, without a control group, researchers generally cannot establish whether reported improvements resulted from EMDR rather than other influences.

A study can therefore provide valuable findings without demonstrating that a treatment caused the reported changes.

This distinction is particularly important when evaluating surveys, observational research, and studies based on participants' own assessments of their progress.

What Are the Limitations of Control Groups?

Although control groups strengthen research, their presence does not automatically make a study reliable.

Several additional factors influence how confidently researchers can interpret the findings.

Group size: Small studies may have difficulty detecting meaningful differences between treatments.

Participant differences: Even with random assignment, groups may differ in trauma history, symptom severity, or other characteristics.

Treatment consistency: Researchers need to consider whether participants received treatments in a reasonably consistent manner.

Outcome measurement: Studies using established PTSD assessment tools may provide different kinds of evidence from studies relying only on general satisfaction ratings.

Follow-up periods: Measuring symptoms immediately after treatment provides different information from assessing whether improvements continue months later.

Another challenge is that participants and therapists generally know which psychological treatment is being provided. This makes it difficult to prevent treatment expectations from influencing experiences and reported outcomes.

Researchers may address some of these concerns by using independent symptom assessors who do not know which treatment a participant received.

How Do Control Groups Help Researchers Understand EMDR's Effectiveness?

Control groups are useful because they help answer questions that symptom improvement alone cannot resolve.

If participants report feeling better after EMDR, that is an important observation. A well-designed comparison study can go further by investigating whether EMDR produced greater improvement than an alternative condition.

Different comparisons contribute different kinds of evidence.

Waiting-list studies help examine whether EMDR performs better than delayed treatment. Usual-care comparisons examine its effects relative to existing care. Active-treatment studies help researchers understand how EMDR compares with other therapeutic approaches.

When results from multiple well-conducted studies are examined together, researchers can develop a more reliable understanding of the treatment's benefits and limitations.

What Is the Main Takeaway?

EMDR researchers use control groups to determine whether improvements are more likely to result from EMDR therapy rather than other factors.

By comparing EMDR with delayed treatment, usual care, or other established therapies, researchers can evaluate treatment outcomes more carefully and draw stronger conclusions about effectiveness.

Control groups are not the only measure of research quality, but they are an important part of the scientific evidence supporting EMDR.

Understanding their purpose can help readers interpret EMDR studies more accurately and recognize the difference between people reporting improvement and research demonstrating a treatment effect.

Conclusion

Control groups play an important role in helping researchers evaluate the effectiveness of Eye Movement Desensitization and Reprocessing (EMDR) therapy. By comparing participants receiving EMDR with those receiving other treatments, usual care, or delayed treatment, researchers can better determine whether improvements are related to EMDR itself.

Research using control groups has contributed to the evidence supporting EMDR, particularly for Post-Traumatic Stress Disorder (PTSD). Although no single study can provide all the answers, findings from multiple well-designed studies help build a clearer picture of EMDR's effectiveness.

Understanding the purpose of control groups makes it easier to interpret research findings and distinguish between reported improvements and evidence that a treatment produces measurable benefits.

References

1. Bisson, J. I., Roberts, N. P., Andrew, M., Cooper, R., & Lewis, C. (2013). Psychological therapies for chronic post-traumatic stress disorder (PTSD) in adults. Cochrane Database of Systematic Reviews, CD003388. Read the systematic review.

2. Effects of EMDR vs. waiting list for adults with post-traumatic stress disorder: A systematic review and meta-analysis of randomized controlled trials. (2026). Journal of Affective Disorders, 392, 120134. Read the study.

3. Sack, M., Zehl, S., Otti, A., Lahmann, C., Henningsen, P., Kruse, J., & Stingl, M. (2016). A comparison of dual attention, eye movements, and exposure only during eye movement desensitization and reprocessing for posttraumatic stress disorder: Results from a randomized clinical trial. View the study on PubMed.