Does a third party observer affect neuropsychological test performance? It depends.

This study is a meta-analysis of available literature examining the effect of an observer on cognitive task performance. Of the 210 identified relevant articles, 62 met inclusion criteria yielding a final sample with 4405 individuals (2496 observed cases, 1909 not observed). The overall effect size was significant (d=-0.24), i.e., the presence of an observer was associated with poorer performance. However results were moderated by the effect size calculation method, cognitive domain, visibility of the observer, and number of observers. Attention, learning/memory, and delayed recall tasks were most adversely impacted by the presence of an observer.