Portfolio.com set out to find the U.S. markets in which income levels have been experiencing strong growth over the long term. Here are the details:

Goal: The study’s objective was to identify the markets with excellent growth rates for per capita income (PCI) during the past quarter-century. PCI is the average amount of money received by each resident (including children) of a specified area during a given year. It encompasses such diverse sources as salaries, interest payments, dividends, rental income, and government checks (including Social Security and welfare).

Areas: The study covered the nation’s 100 largest metropolitan areas. They ranged from New York City, with a metropolitan population of 19.07 million as of 2009, down to Daytona Beach, Florida, with 495,890 residents.

Sources: Raw per capita income figures came from the U.S. Bureau of Economic Analysis. Figures for the most recent year available, 2009, were released in August 2010. All growth rates were calculated by Portfolio.com.

Factors: Portfolio.com used a 25-part formula to analyze the consistency and strength of PCI growth in each market. The formula compared each area’s growth rates against the U.S. averages for 25 different time spans, yielding an overall score for income growth. All 25 spans ended in 2009, ranging in length from 25 years (1984-2009) to a single year (2008-2009).

Availability: Selected growth rates for each market are provided in chart form with this report. Space limitations prevented the publication of rates for all 25 intervals.

Formula: Each area’s rates were compared against the corresponding averages for the study group in all 25 categories, a process that rewarded markets that had long-term records of solid growth. Above-average performances received positive scores, while below-average results were given negative scores. Each area’s 25 category scores were totaled to determine its overall rank. Total scores ranged from 54.01 points for El Paso, Texas, to negative-48.81 points for Atlanta.

Get more business intelligence from Portfolio.com:

• For a Few Dollars More: El Paso residents earn among the lowest wages in the country. But a closer look at the city's economics unveils a source of pride: record income growth that's unmatched by the nation's largest metro areas.
• Boom Turns to Bust: California, Nevada, and Florida ranked among the nation's most robust economies five years ago. But since the real estate bubble burst, the leaders have become the laggards.
• Rich City, Poor City: It’s no secret we live in a country of haves and have-nots. But did you know there’s a California city where nearly 29 percent of households earn more than $200,000 a year, while in one Pennsylvania city, not a single household makes that amount?