The selection of Cardinal Jorge Mario Bergoglio of Argentina as the new pope, Francis, was largely unexpected by betting markets and Vatican experts, in part because of his advanced age. Cardinal Bergoglio, 76, is probably the ninth oldest of the 266 popes at the time of his election, accounting for some uncertainty because the age of many early popes remains unknown, wrtites Nate Silver in The New York Times.

As a matter of actuarial science, Francis is not likely to have an especially long tenure. The nine previous men who were known to be 75 or older at the time of their election to the papacy served for an average of only five years.

That may be too pessimistic an estimate in the case of Francis: it is based on a small sample size and does not account for modern improvements in health and medical science. Acknowledging that there are considerable lifestyle differences between an Argentinian pope and an average American citizen, the life expectancy for a 76-year-old American man is now about 10 additional years.

Of course, Francis could follow Benedict XVI’s precedent by resigning the papacy before his death. It is probably safe to say that a tenure shorter than five years would be considered brief for Francis, while a regime of much more than 10 years might be unexpectedly long.

The cardinals who elected Cardinal Bergoglio are probably not looking up actuarial tables, but they presumably have some intuition about how long his papacy might last. So one question is whether they saw his advanced age as a liability — or an asset.

How might Francis’ age be advantageous? One reason is that, if he were to serve 5 to 10 years, that would actually be very well in line with historical precedent . Beginning with St. Peter in 33 A.D., there have been 266 popes in 1,980 years, or about one new pope every seven and a half years. Benedict XVI’s regime, which lasted for seven years and 315 days before ending in February, was also well in line with this historical average.

The Roman Catholic Church has gone through different fashions in the ages of its popes. They rose steadily throughout the 16th and 17th centuries, culminating with the selection of the 79-year-old Clement X in 1670. However, as the chart below suggests, there was also a very considerable increase in the life expectancy of popes during this period.

Popes were starting their pontificates at a later age, but also ending them at a later age; thus, there was little change in the length of their papacies, which averaged about seven years.

FULL STORY For cardinals, there are advantages in choosing an older pope (NYT)