A Top 10 Worst List San Diego Did Not Make

We may have our financial woes and corruption scandals, but San Diego is not the most irregular city in the US. From Slashfood:

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Dannon's new yogurt, Activa, contains a special bacterial culture known as Bifidus Regularis that helps to regulate the digestive tract. To help promote their new product, and perhaps to locate potential markets for this breakfast-food-come-Milk of Magnesia-competitor, Dannon commissioned a survey to determine the most irregular cities in America. The survey defined irregularity as not going to the bathroom for two or more days and found that the ten most irregular cities are:

1. Orlando, FL
2. Memphis, TN
3. Greenville, NC
4. Tampa, FL
5. Raleigh-Durham, NC
6. San Antonio, TX
7. Oklahoma City, OK
8. Jacksonville, MI
9. Miami/Fort Lauderdale, FL
10. Philadelphia, PA

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What I want to know is, how did they determine which cities are most irregular? I can't think of a single source of that information.