How does one compute the "Donovan Index"?

[zamboniracer]

In the Philly sports v. Pittsburgh sports thread there is a reference to The Donovan Index which purports to be the "ultimate ranking of cities regarding major professional sports championships." My problem is that I can't figure out Donovan's math.

Donovan says,

"The Formula for the Donovan Index is a simple mathematical equation that accurately determines the rate at which cities' teams, and by extension cities, win championships in major sports leagues. The equation for a team (we'll use the 76ers) would be as follows:

Sum of the number of teams in NBA in 76ers' championship seasons divided by
Number of Seasons that the 76ers have played

Lets make our example concrete.

Since entering the NBA in 1963-64, the Philadelphia 76ers have won the NBA title twice, in 1967 and 1983. The two championships are not equal, however. In 1967, the NBA had 10 teams; in 1983, it had 23. This discrepancy is known as the "Riordan Factor". We thus award the 76ers 10 points for their first championship and 23 for their second. We determine their index score by adding 10 to 23 and dividing the sum by 44 seasons:

(10 + 23)/ 44 = 0.75

It thus follows that an "average" score is 1.00. In a ten-team league, a team should win once every ten years. Ten teams divided by ten seasons equals one. The 76ers score a 0.75; they don't quite win titles at an average rate. The city of Philadelphia scores a 0.69. It's that simple."

What isn't simple to me is how Donovan combines the 76ers's score, with the Phillies', Flyers' and Eagles' to arrive at 0.69 for Philadelphia's total score.

(Note: that's leaving aside whether or not Donovan included the Philadelphia A's of MLB and the Philadelphia Warriors of the BAA/NBA).

Any help from math/stats whizzes would be appreciated.

[Blaster Master]

It appears to be a weighted average using the same math... sum up the total points across all teams and the total seasons and you get the 0.69. Look at the page specific to Philadelphia...
http://www.donovanindex.com/citiesI/philadelphia.php

[cmkeller]

Strange that they didn't count the Philadelphia A's as beginning in 1901, or the Phillies in 1883.

[anson2995]

Originally Posted by cmkeller

Strange that they didn't count the Philadelphia A's as beginning in 1901, or the Phillies in 1883.

The formula is based on league championships, and as such Donovan does not include baseball seasons that did not culminate in a world series.

As a football historian, I can't reconcile his decision to start counting NFL seasons in 1921. If his criteria is in fact championships won on the field (as opposed to simply finishing first in the standings at the end of a regular season), then he ought to start in 1932. If it were me, I'd count AFL/NFL titles from 1967-1969 too, but these are probably minor quibbles.