The 50% number is a bit mysterious, but if I understand the text of the article correctly, it essentially means that if we do not account for the noise added by accidents and such, we get a Pearson correlation of life expectancies of monozygotic twins of ~0.23. If we correct for accidents, the correlation rises to 0.5, hence 50% (with some further analysis they go up to 0.55, hence "above 50%" in the abstract). Now, in practical terms, this means that, given a MZ twin who died recently of natural causes, we could obtain an estimate for ourselves, but only if we make additional assumptions. A correlation coefficient alone is not very informative.
>Now, in practical terms, this means that, given a MZ twin who died recently of natural causes, we could obtain an estimate for ourselves,
Uh... am I misreading your comment, or are you suggesting that when your identical twin dies of non-accidental death, you can be pretty sure you're about to croak in the next wee days or weeks yourself? Very difficult to engineer that alarm bell (you either have a twin, or not), and too damned late to matter.
With a correlation of ~0.5 the window will be much wider than weeks or months, and it's more like, "If your MZ twin died of completely natural causes at 70, it is unlikely that you will live to 120."
