	Introduction

Individuals were first able to establish health savings accounts (HSAs) in 2004. These accounts allow people to pay for out-of-pocket medical expenses on a tax-advantaged basis. Individuals must have a qualifying high-deductible health plan (HDHP) to establish an HSA. Even though HRAs are also used to pay for unreimbursed medical expenses on a tax-advantaged basis, only employers may establish and contribute to an HRA. Data covering enrollment and/or cost sharing during the first few years of HDHPs and their associated HSAs are now available from at least five separate sources. Only one source provides data on HSAs. Two sources provide data on HDHPs whose owners are eligible to open an HSA. The remaining two sources provide data that include individuals with HRAs. The primer also provides the most recent data available from each source on enrollment, premiums, and deductible. The data from America's Health Insurance Plans (AHIP) are obtained from insurance plans and measure all covered lives in the plans. Four of the sources contain data on enrollment. No other data source provides breakdowns for more than one of these markets. Nevertheless, the data sources differ in the insurance markets analyzed; whether the information covers HSAs, HSA-eligible HDHPs, or HSA-eligible HDHPs and HRAs; and whether the information is provided by employers, insurance companies, or individuals. Great caution should be exercised in any attempt to combine data from these different sources. A more fruitful strategy would be to decide on a specific question and use only the source which best answers that question.
Individuals began establishing health savings accounts (HSAs) in 2004. These savings accounts are generally used to pay for unreimbursed medical expenses on a tax-advantaged basis. Any unspent money accrues to the individual. To open an HSA, the individual must enroll in a qualifying high-deductible health plan (HDHP). HSAs are tax-advantaged and provide some incentives for people to monitor, and perhaps reduce, their expenditures on health care.
Data covering enrollment and/or cost sharing during the first few years of HDHPs and their associated HSAs are now available from at least five separate sources. This primer provides information on the data sources, together with the most recent data available from each source on enrollment, premiums and deductibles.
Only one source, the Internal Revenue Service, provides data on HSAs. These data count the number of tax filing units that took a deduction for the HSA on their tax returns. Two sources provide data on HDHPs whose owners are eligible to open an HSA. One of these data sources, from the American Health Insurance Plans, is a census of virtually all lives covered by a HSA-eligible HDHP. The remaining two sources provide data that includes individuals with another type of health-related savings account (the Health Reimbursement Account).
In addition to differing by the type of insurance plan covered, the data sources differ in the insurance markets analyzed, and whether the information is provided by employers, insurance companies, or individuals. Great caution should be exercised in any attempt to combine data from these different sources. A more fruitful strategy would be to decide on a specific question and use only the source which best answers that question.