Key finding
Helmet use mortality OR ~0.48 in recent meta-analysis; other cohorts ~0.65
Evidence & causal status
Strong for helmet protection; insufficient for riding itself
Strong for helmet intervention; riding-vs-nonriding mortality effect not cleanly estimated
Caveats & limitations
Reliability / bias notes: Confounding by riding behaviour, speed, alcohol, road exposure; helmet evidence often crash-conditioned
This describes a population-level association from published research. It is not a prediction about any one individual, and association is not the same as causation unless stated otherwise above.