The effect of placebo in split-scalp and whole-head platelet-rich plasma trials for androgenetic alopecia differs: Findings from a systematic review with quantitative evidence syntheses.

The association between design (i.e., split-scalp vs. whole-head) and outcome, in placebo arms of AGA trials on PRP monotherapy, had never been reported. This "design effect" could partly reconcile the incongruent conclusions across the PRP literature for AGA; furthermore, clinical guidelines can consider "design effect" when selecting evidence to base care practices on.