There were four centenarians on last year's list, and only one of them (25 %) snuffed it. The succes ratio on the entire list was 26 %, so picking the extremely old is actually decreasing the odds, though only slightly.
don't be stupid...
I won't, thank you.
You obviously did not get my point, so I'll give it another try. Picking a 100-year-old celebrity just because of his age has not proved to be a 'guarantee for succes' as Mr Macabre stated. In fact, if we take last years' list, the odds of a centenarian dying have turned out to be even slimmer than those of the list as a whole. This is, of course, not because centenarians can not be expected to die soon, but because most of the other picks were selected because of their frail health, life-threatening diseases or specific habits that tend to shorten their life-expectancy. The examples of Ruby Muhammad and Brooke Astor prove that some centenarians might still have some years to go. They must have been quite strong and healthy just to have made it to their impressive age, after all.
Edit: Of the seventeen centenarians that were picked on the last ten lists, seven died in that particular year. Quite a good score, you might say, but we only scored heavily with them in 2003 and 2004, with 5 hundred-years-old dying in that particular two years (out of 8 picks).
Age must be a factor, as must no. of appearances - Clive Dunn is heading towards a very precarious number of appearances (think 13 is most?). I reckon, over 100, over 10 appearances and a recent serious illness would put someone in the Dead Cert category. Perhaps there is a formula that applies - e.g. Age + (2 x appearances) + bonus if recently serious ill.
