Information was collected on "any plan" for 1976 and 1980; on to up to five plans in 1982; on up to six plans in 1983; on up to five plans for 1984-1989; on "any plan" for 1990 and 1991; and on up to four plans per family for 1992 forward. Beginning in 2004, the NHIS public use files reported data only for plans one and two.

Persons with three or more plans have a "yes" response in HIPRIVGT2 (available for 2004 forward). Analysis by IHIS staff indicates that a very small number of persons (less than 0.2 percent of the total number of individuals with private health insurance per year for 2004 to 2009) had three or more private insurance plans.

For all years except 1993-1996, single service plans and plans that pay only for accidents were not considered to be health insurance.

For 1976 to 1989, plans that paid "extra cash" for hospital stays were considered to be health insurance, while for 1992 forward, they were not.

For 1993 to 1996 only, having just a single service plan was treated as having health insurance.

For 1999 forward, a separate category for single service plans was added to the flashcard listing types of insurance coverage, which further distinguished single service plans from comprehensive private health insurance.

For 1976 to 1989, the Field Representative's Manuals defined private insurance as "specifically designed to pay all or part of the hospital, doctor, surgeon, or other medical expenses of the insured individual" (including dentist expenses for 1989 and 1986). The Manuals further noted, "The plan, in order to be considered as insurance, must be a formal one with defined membership and benefits. Include Health Maintenance Organizations (HMOs) and Individual Practice Associations (IPAs), such as Kaiser, Group Health, etc."

For 1990 forward, the Manuals defined private health insurance to be any type of health insurance, including Health Maintenance Organizations (HMOs), other than the public programs of Medicare, Medicaid, Military health care/VA, CHAMPUS/TRICARE/CHAMP-VA, Indian Health Service, state-sponsored health plans, CHIP (the Children's Health Insurance Plan, beginning in 1999), and health insurance from other government programs.

For 2001 forward, the Manuals indicated that insurance coverage through COBRA (the Consolidated Omnibus Budget Reconciliation Act of 1985) or by
TCC (Temporary Continuation of Coverage) should be considered private health insurance (obtained through an employer or workplace).

For 1997 to 1999, only people with an affirmative answer to this initial question have responses to follow-up questions about the kind of health insurance and the details of coverage; for 1997 to 1999, those who did not answer the initial question affirmatively are coded NIU (not in universe) for follow-up question on insurance characteristics. Beginning in 2000, the response "no insurance" was included as a valid response to the initial question. Thus, for 2000 forward, the universe for follow-up questions on insurance coverage type and details was "all persons" (including those with an affirmative response to HINONE or "no insurance").

2004 forward:

• Which one of these categories best describes how this plan was obtained?
• Response categories: Through employer; through union; Through workplace

• Was this plan originally obtained through the workplace, such as through a present or former employer or union?

• (Not counting the government health programs we just mentioned,) In (month) was anyone in the family covered by a private health insurance plan?

• Was this plan originally obtained through the workplace, that is, through a present or former employer or union?

• (Not counting the government health programs we just mentioned,) In (month) was anyone in the family covered by a private health insurance plan? Do NOT include plans that pay for ONLY ONE type of service, such as nursing home care or accidents.

• Was this plan obtained through an employer or union?

• Health insurance can also be obtained privately or through a current or former employer or union. Was anyone in the family covered by private health insurance or by membership in a health maintenance organization in (month)?

• Was any of [name] health insurance obtained through an employer or union?

• (Not counting Medicare), is anyone in the family now covered by a health insurance plan which pays any part of hospital, doctor or surgeon's bill?

• Was this plan originally obtained through the workplace, that is, through a present or former employer or union?

• Is anyone in the family covered by hospital insurance, that is, a health insurance plan which pays any part of a hospital bill?

• Is anyone in the family now covered by a health insurance plan which pays any part of hospital, doctor or surgeon's bill?

• Was this plan obtained through an employer or union?

During the course of data editing, the NCHS discovered many errors in the responses to questions about insurance coverage. This might be shown, for example, by a mismatch between the verbatim name of an insurance plan and the type of insurance coverage the person selected from the categories on a flashcard. (See the variable description for HINOTCOVE for a description of this back-editing process.)