To the Editor: In their randomized controlled trial, Dr Lautenschlager and colleagues1 investigated the effect of physical activity on the cognitive function of older adults at risk for Alzheimer disease. We have some concerns about the study design.
First, the placebo effect was not investigated in this trial. Participants were not blinded to group assignment and those in the physical activity group may have had more confidence in performing the cognition test because they were aware that they were in the intervention group. Previous studies have found that confidence can enhance the performance on cognition tests.2
Wu S, Liang J, Miao D. Physical Activity and Cognitive Function in Alzheimer Disease. JAMA. 2009;301(3):272-274. doi:10.1001/jama.2008.1011