Evidence quality
Reverse causation
When the apparent outcome may actually influence the exposure, reversing the assumed direction.
What it means
Definition
Reverse causation. Reverse causation is a key limitation in observational research. It occurs when early disease, symptoms or behaviour changes influence the measured exposure.
What it can tell you
It can help separate an observed association from a tested causal claim.
What it cannot tell you
It cannot remove confounding or prove causation without stronger study design and analysis.
Headline trap
Why this matters in headlines
People may reduce activity because they are already unwell, making inactivity look like the sole cause of illness.