How long do Popes usually serve?

Yesterday Pope Benedict XVI announced his imminent resignation from the Papacy, to the surprise of millions (if not Billions) of people. His reign as leader of the Catholic church feels very short for two reasons:

1) he is the first Pope for several hundred years to resign
2) his predecessor was the second longest serving Pope in history

For those of us young enough to not remember a time before Pope John Paul II, the 8-year reign of Benedict XVI feels particularly brief. I then wondered: how many years on average does a Pope reign?



The average duration turns out to be... 7.3 years (median of 6 years). Additionally, there's no strong increase in length of reign over time. In other words: despite lifespans increasing, Popes still tend to have a short tenure. It appears Benedict XVI really isn't too far off the average!

I then thought to compare these numbers with another distinguished group of (historically) men: Justices of the Supreme Court of the United States. Fun fact: there have been a total of (including those currently serving/reigning) 113 Supreme Court Judges, 264 Popes. These justices have an average service on the bench of 16.4 years (median 16 years)!


To compare these two populations of people, I have reverse-sorted their durations of service in to cumulative distributions. The way to read this diagram is: 60% of Popes reign 10 or more years, and less than 20% of Popes serve 20 years or more.  By contrast, 65% of Justices serve 20 years or more.

Cumulative distribution for the years of service of Popes and US Supreme Court Justices.

Update:
Some people were curious about the raw distributions of Popes vs Justices...