No proven nine-year boost for right-handers

The claim that right-handers live nine years longer came from a 1991 study comparing ages at death in a sample from a particular year. A later analysis showed that the result can be explained by historical changes in how often left-handedness was acknowledged and reported: older generations included people who had been pressured to switch or were not counted as left-handed. This is not evidence that handedness itself determines lifespan.