# Placebo effects are weak: regression to the mean is the main reason ineffective treatments appear to work

Jump to follow-up "Statistical regression to the mean predicts that patients selected for abnormalcy will, on the average, tend to improve. We argue that most improvements attributed to the placebo effect are actually instances of statistical regression." "Thus, we urge caution in interpreting patient improvements as causal effects of our actions and should avoid the conceit of assuming that our personal presence has strong healing powers." McDonald et al., (1983) In 1955, Henry Beec