1 The plans fall under the provisions of the Employee Retirement and Income Security Act (ERISA) of 1974.

2 In all versions, AHPs would be subject to the provisions of the Health Insurance Portability and Accountability Act (HIPAA), which among other things makes health insurance "guaranteed issue" in the small group market.

3 "Horizontal Merger Guidelines," U.S. Department of Justice and the Federal Trade Commission, Washington, D.C., April 2, 1992.

4 They are usually derived by stating a firm's market share as a percentage of the total receipts for a given NAICS (North American Industry Classification System) code. One such source is the U.S. Census Bureau (USCB) Health Care & Social Assistance - Subject Series, Table 6a. "Concentration by Largest Firms Subject to Federal Income Tax: 1997" and Table 6b. For those firms that are not subject to federal income tax, it contains information regarding the number of establishments, receipts - amount and percent of total, annual payroll, first quarter payroll, and number of paid employees. This study uses the NAICS codes for industry number 62 and its respective subcategories. Table 3.1 in the text was adapted from USCB Table 6a.

5 For example, when the top five firms represent 90 percent of the market, the Four-Firm Concentration Ratio is at least 72 percent and the Herfindahl-Hirshman Index is at least 1,296.

6 Some states have passed laws mandating insurance rate bands, whereby insurers are limited in their ability to charge rates based on actuarial risk. For instance, such laws might mandate that the sickest individuals cannot be charged more than 50 percent more than the average rate and the healthiest cannot be charged less than 50 percent of the average rate. Grouping people with diverse actuarial risks in more closely banded pools results in a cross-subsidy, whereby the young and healthy are charged more than the expected cost of their care so that older or less-healthy individuals can pay less than the expected cost of their care.