The Pervasive Problem With Placebos in Psychology

Abstract

To draw causal conclusions about the efficacy of a psychological intervention, researchers must compare the treatment condition with a control group that accounts for improvements caused by factors other than the treatment. Using an active control helps to control for the possibility that improvement by the experimental group resulted from a placebo effect. Although active control groups are superior to “no-contact” controls, only when the active control group has the same expectation of improvement as the experimental group can we attribute differential improvements to the potency of the treatment. Despite the need to match expectations between treatment and control groups, almost no psychological interventions do so. This failure to control for expectations is not a minor omission—it is a fundamental design flaw that potentially undermines any causal inference. We illustrate these principles with a detailed example from the video-game-training literature showing how the use of an active control group does not eliminate expectation differences. The problem permeates other interventions as well, including those targeting mental health, cognition, and educational achievement. Fortunately, measuring expectations and adopting alternative experimental designs makes it possible to control for placebo effects, thereby increasing confidence in the causal efficacy of psychological interventions.

On the validity and generality of transfer effects in cognitive training research

“…These predictions can only be made on the basis of good conceptual and empirical knowledge of the matter, which may not always be available from the start. Additionally, the presence of subjective transfer models may interfere with the theoretical assumptions and -if not properly addressed -may lead to false alarms as well as false negative results (Boot et al, 2013). Finally, latent factor models of cognitive constructs come with additional implications.…”

“…7 control condition respectively (e.g., Shipstead et al, 2012;Redick et al, 2013, but see Boot et al, 2013). Following this logic, all participants would receive challenging interventions but one focusing on one ability (e.g., working memory) and the other focusing on another ability (e.g., processing speed).…”

“…Thus, additional measures may be needed to account for the effect of subjective transfer models. Possible measures have been described recently (see Boot et al, 2013) and will not be further discussed here.…”

Treatment expectations but not preference affect outcome in a trial of CBT and exercise for pain

“…3 And in randomized trials where an active placebo control group is used as a comparator, they should be chosen to match the treatment group for expectations of effectiveness. 30 …”

Video Games as Tools to Achieve Insight into Cognitive Processes

“…Cain et al (2014) and Pohl et al (2014) in this Research Topic present evidence in favor of cross-sectional differences between action gamers and non-gamers on measures of vision and attention. However, evidence from cross-sectional and training studies used to support action game effects has been criticized for a variety of methodological reasons (Boot et al, 2011(Boot et al, , 2013bKristjánsson, 2013;Bisoglio et al, 2014;Ferguson, 2014). Importantly, Cain et al (2014) and Pohl et al (2014) provide a full report of their methods and the ways in which participants were recruited, following the best reporting practices outlined by critics of game effects.…”