Portfolio.com/bizjournals has devised a formula to gauge future expansion or relocation possibilities in professional sports. Here are the details:

Structure: Our system is based on total personal income (TPI), the sum of all money earned by all residents of an area in a given year. We used official TPI data from 2008, the latest year for which statistics are available from the U.S. Bureau of Economic Analysis.

Figures for Canadian markets are Portfolio.com/bizjournals’ estimates for 2008 (in American dollars), based on raw data from Statistics Canada.

Our study covers the 81 markets in the United States and Canada with TPI in excess of $25 billion, as well as Green Bay, Wisconsin, the only market below that threshold to have a major-league team.

Available income: We focused on expansion or relocation potential within five leagues:

• Major League Baseball (MLB)
• National Football League (NFL)
• National Basketball Association (NBA)
• National Hockey League (NHL)
• Major League Soccer (MLS)

We used team revenue data and average ticket prices to calculate the amount of TPI needed to adequately support a team in each league. Minimum income bases were estimated to be $86.7 billion for MLB, $37.3 billion for the NFL and NHL, $36.4 billion for the NBA, and $13.9 billion for MLS.

We then calculated each area’s available personal income (API) by subtracting the TPI needed to support the market’s existing teams. Philadelphia, for example, has TPI of $274.1 billion. But its four existing franchises (MLB, NFL, NBA and NHL), along with an MLS expansion team that will begin play next year, need a base of $211.6 billion, resulting in API of $62.5 billion.

If an area’s API is expressed as a negative number, the market is said to be overextended. Teams in secondary professional or minor leagues were not counted against a market's API. Nor were college teams.

Capacity scores: Our final step was to determine market capacity ratings for every area, using a 100-point scale. Ratings are based on a market’s percentage of the necessary API for a given sport.

A score of 100 indicates that a market’s income base is strong enough to support a team in a specific league. A score between 70 and 99 is a sign of a borderline income base, meaning that a market may or may not be able to support a franchise, depending on the team’s ability to reach fans beyond the metro area’s boundaries. A score below 70 indicates that an income base in insufficient for a given sport.

Keep in mind that a market's scores for all sports would change if it were awarded a new franchise in one of them, since its API would be reduced.

Our formula focuses on open markets, which is why we did not produce capacity scores for any area that already has a team in a given league. It’s always possible that the NFL might want to put a third team in New York City someday, for example, but such a move is certainly not on the front burner today.