Theory 08/The rival is a confound/Clinical trials
Placebo or Regression?
The claim
Placebo response in pain trials reflects genuine expectancy effects.
01The rival explanation
Patients enrol at symptom peaks, so improvement follows from regression to the mean regardless of expectation.
02What would tell them apart
Regression predicts symmetric improvement in patients enrolled at peaks and in those enrolled at random times; expectancy predicts improvement only where belief is manipulated.
03Prediction
Improvement should scale with baseline severity only in expectancy conditions.
04Refutation
If improvement tracks baseline severity regardless of expectancy, the rival wins.