Evidence-appraisal glossary
Reverse Causation
When the outcome actually causes the exposure rather than the other way around, making a real association point in the wrong direction. Often the developing disease changes a behavior or a measured factor before it is diagnosed.
Also called: reverse causality, protopathic bias.
Reverse causation is a frequent trap in observational studies, especially cross-sectional ones that measure exposure and outcome at the same moment. Low cholesterol, for example, may appear linked to cancer not because it raises risk but because early undiagnosed cancer lowers cholesterol. A short interval between exposure and outcome is a warning sign, and a common safeguard is to exclude events in the earliest period of follow-up or to use a design less vulnerable to this ordering.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.