Quantifying the Difference Between Active and Passive Control Groups in Cognitive Interventions Using Two Meta-analytical Approaches

Abstract

Despite promising reports of broad cognitive benefit in studies of cognitive training, it has been argued that the reliance of many studies on no-intervention control groups (passive controls) make these reports difficult to interpret because placebo effects cannot be ruled out. Although researchers have recently been trying to incorporate more active controls, in which participants engage in an alternate intervention, previous work has been contentious as to whether this actually yields meaningfully different results. To better understand the influence of passive and active control groups on cognitive interventions, we conducted two meta-analyses to estimate their relative effect sizes. While the first one broadly surveyed the literature by compiling data from 34 meta-analyses, the second one synthesized data from 42 empirical studies that simultaneously employed both types of controls. Both analyses showed no meaningful performance difference between passive and active controls, suggesting that current active control placebo paradigms might not be appropriately designed to reliably capture these non-specific effects or that these effects are minimal in this literature. Keywords Placebo effects . Hawthorne effects . Experimental confounds . Cognitive training . Meta-analysisBeing able to make causal claims is a primary goal of experimental scientists. A strong demonstration of causality usually entails both a clear temporal relationship between two variables (i.e., cause precedes effect), as well as the manipulation and isolation of a single causal factor (i.e., two comparison groups that are completely matched on all variables save the one of interest). The former criterion is generally easy to satisfy in experimental studies, but the latter can be more elusive.

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