Much has been written and said about the supposed difference in life expectancy due to handedness. The particular theory which claims an enormous gap of nine years is frankly highly implausible for several reasons, chiefly being first that not nearly enough people die in accidents or due to stress related to left handedness to make such a huge 9 year difference, and second, the study almost certainly neglected to take into account the decreasing cultural bias and pressure (in America at least) against left handedness, and the resulting decrease in "forced" or pressured conversions to right handedness over ages. For example, surveys will naturally show a much larger percentage of right handers in their 70's and 80's vs. right handers in their 20's or 30's because the incidence of left-to-right conversions is clearly much lower in the latter cohort. The "missing" left handers creates the mistaken impression of higher mortality rates.

The best longitudinal data in existence on left and right handers' lifespans is probably US Major League Baseball statistics (glad that insufferably boring game is good for something!), which have meticulously tracked the full careers and future lives of thousands of left and right handed baseball players throughout the 20th century. This data gives an overall net difference in life expectancy of 8 months (advantage for right handers), which is certainly much easier to swallow than 9 years.

Finally, if lefties were really dropping dead 9 years earlier, don't you think insurance companies would be all over this, and incorporating the difference in their premium rates?? They're not, and that should tell you something.