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Dear Drs. Dave and Dee,
What are the statistics on the life expectancy of left-handed people?
Signed,
Need to Know
Dear Need to Know,
Life expectancy of left-handers and right-handers are the same (see links below).
There was a controversial study done in 1980 by Halpern & Cohen that suggested left-handed people had an average life expectancy of 9 years less than right-handed people. Data was based on second-hand information: surveys from the next-of-kin of recently deceased persons asking about right/left handedness and age of death. They found left-handed average age of death was 66; right-handed average age was 75.
Unfortunately, this study keeps getting quoted even though more recent data has shown their hypothesis is not supported. Second hand survey data is not a sound methodology.
In addition, if a study reports a higher mortality rate (or any other "problem") in left-handers, then it's very important to look at the research design and how the data was analyzed. Simply checking the sample sizes will give a good indication of whether it was a "real" significant difference. If the sample sizes are large, and most studies have sample sizes of 1,000 or more, then there will be a "statistically" significant difference between groups (i.e.: Left versus Right) even if the amount of variance explained by the two groups is very small, which means there is no clinical significance. A statistical significant difference does not mean it has clinical or meaningful significance. Many statistical tests will give a significant difference only because of large sample sizes. Therefore, the measure of explained variance needs to be computed because it is unaffected by sample size.
