Evidence-appraisal glossary
Healthy-user effect
The healthy-user effect is a confounding pattern in observational studies where people who take a preventive treatment or attend screening tend to be healthier and more health-conscious than those who do not. Their better outcomes may reflect that lifestyle rather than the treatment.
Also called: healthy-adherer effect.
The healthy-user effect biases observational comparisons because adherence to a preventive measure travels with other favorable habits like exercise, diet, and regular care that independently lower risk. A related version, the healthy-adherer effect, is shown by findings that good adherence even to a placebo predicts better outcomes. It is a reason observational associations between preventive therapies and benefit can be misleading, and why randomized trials remain the stronger test.
Read the full Reading the Evidence blog.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.