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A critical decision in experimental research is what to do with participants in the control group. Some researchers compare the treatment group to a no-treatment control group. In this type of study, participants in the control group get no treatment whatsoever. The main problem with using a no-treatment control group is that it is unethical to deny treatment to children with mental health problems. By withholding treatment from children with ADHD, we might be contributing to their attention and behavior problems at home and school.

A potential solution is to delay treatment for a short period of time instead of denying it altogether. In this case, researchers compare participants in the treatment group to participants assigned to a waitlist control group. Treatment is delayed to children assigned to the waitlist, but not altogether withheld. At the end of the study, children on the waitlist are also allowed to participate in treatment. Waitlist control groups can be an ethical way to evaluate the efficacy of therapy (Table 3.2).

Table 3.2

Note: Based on Sorger and colleagues (2020).

For example, in another study, researchers randomly assigned children with ADHD to either a neurofeedback treatment group or to a waitlist control group. As before, researchers assessed children’s outcomes by asking their parents to rate attention problems before and after the study. As expected, the parents of children in the treatment group reported a significant reduction in symptoms, whereas the parents of children in the control group did not. At the end of the study, children on the waitlist were also provided neurofeedback (Cortese et al., 2017).

Both no-treatment control groups and waitlist control groups suffer from another shortcoming: participants know that they are either receiving treatment or serving as controls. This knowledge can affect their behavior during the study and their perceptions of improvement. The placebo effect refers to people’s tendency to improve simply because they know that they are receiving treatment and they expect the treatment to work. Researchers must control for the placebo effect; they need to be able to attribute symptom reduction to the treatment itself, not to people’s awareness that they are receiving treatment or their belief that they will get better (Thibault et al., 2017).

To reduce the placebo effect, researchers use an attention-placebo control group. In an attention-placebo controlled study, participants assigned to the control group receive a theoretically inert form of “treatment” that resembles the therapy received by participants in the actual treatment group. In medical research, participants might take a pill that looks like the actual medication but has no active ingredients. In psychological research, participants might talk with a therapist about day-to-day events, but not receive any form of real therapy. Participants in the attention-placebo control group would likely believe that they were receiving actual treatment, thereby controlling for the placebo effect.

For example, researchers compared children with ADHD who participated in neurofeedback to another group of children randomly assigned to receive “sham” neurofeedback. Children in the sham condition were connected to an EEG and they played neurofeedback games identical to children in the treatment group. However, the feedback that they received was random and not associated with their actual brain activity. Because these children and their parents believed that they were receiving actual neurofeedback, the researchers were able to control for the placebo effect. Surprisingly, the parents of children who received actual neurofeedback reported only slightly better outcomes than the parents of children who received sham neurofeedback. These findings tell us that the benefits of neurofeedback were largely explained by placebo, rather than by neurofeedback itself (Arnold et al., 2013).

A final option is to compare participants who receive a new treatment to treatment as usual (TAU). Participants assigned to a TAU control group are referred to clinicians in the community and receive whatever care these clinicians provide. Use of a TAU control group is the most stringent test of a new form of therapy. The new treatment must show that its benefits match or exceed those offered by existing therapies.

For example, researchers randomly assigned children with ADHD to two conditions. Youths in the first condition received stimulant medication (TAU). Youths in the second condition received neurofeedback. Parents reported significantly greater improvement among children prescribed medication than children receiving neurofeedback. Moreover, teachers who did not know that children were receiving treatment reported significant improvement in children taking medication but no improvement in children receiving neurofeedback. The researchers concluded that medication is superior to neurofeedback and that many of the effects of neurofeedback are explained by parents’ expectations (Gelade, Janssen, Bink, Maras, & Oosterlaan, 2016).

Randomized controlled trials can be open label or blind. In an open-label study, participants and researchers know which participants are receiving treatment and which have been assigned to the control group. An open-label study gets its name because, in medical research, participants can see the name of the medication they are receiving on the label of the bottle. Open-label studies increase the chance that people’s biases might influence the study’s outcome. For example, children might alter their behavior or parents might perceive greater improvement if they know that children are receiving treatment.

In a double-blind study, neither participants nor researchers know to which group participants have been assigned. Double-blind studies reduce bias by treating both groups of participants equally and keeping researchers in the dark regarding each participant’s treatment status.

Review

 An experiment is a specific type of study in which participants are randomly assigned to two or more groups, at least one independent variable is manipulated in one of the groups, and all other factors are held constant. Experiments allow us to make statements about causality.

 Attention-placebo and treatment as usual (TAU) control groups can reduce the placebo effect, that is, people’s tendency to improve because they know they are receiving treatment and they expect it to work.

 Double-blind studies reduce biases in experiments. Neither researchers nor participants know to which group each participant has been assigned.