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.