the typical gap

Reviewing possible causes of aging Atul Gawande drops this little statistic:

Only six per cent of how long you’ll live, compared with the average, is explained by your parents’ longevity.

So “good genes” aren’t it?

Even genetically identical twins vary widely in life span: the typical gap is more than fifteen years.

Huh? Really?

Gawande doesn’t source that one (unless it’s from the same Max Planck institute for Demographic Research in Rostock, Germany that he attributes the 6% figure to).

15 years? What’s the “typical gap” between non-identical twins or age disparate siblings? I would have thought it much closer than 15 years. What does he mean “typical”? He doesn’t use the word “average” so does he not mean the mean? Maybe he means the median – half of all twins live 15 years longer than the dead twin, half of all twins live fewer than 15 years longer. Or the mode? Most twins who lose a twin live 15 more years. Or, rather, “more than fifteen”.

A mysterious number.

source: The New Yorker, April 30, 2007