Interviewers first asked, "Are you covered by health insurance or some other kind of health care plan?" Respondents were instructed to "Include health insurance obtained through employment or purchased directly as well as government programs like Medicare and Medicaid that provide medical care or help pay medical bills." Individuals who had answered affirmatively were asked, "What kind of health insurance or health care coverage do you have?" Respondents selected the appropriate response from a card listing various types of insurance coverage:

• Private health insurance (2004 forward)

• Private health insurance plan from employer or workplace (1997-2003)

• Private health insurance plan purchased directly (1997-2003)

• Private health insurance plan through a State or local government program or community program (1998-2003)

• Medicare (1997 forward)

• Medi-Gap (1997 forward)

• Medicaid (1997 forward)

• CHIP (Children's Health Insurance Program) (1999 forward)

• Military Health Care/VA (1997-2003)

• Military Health Care (CHAMPUS/TRICARE/CHAMP-VA) (1997 forward)

• Indian Health Service (1997 forward)

• State-sponsored health plan (1997 forward)

• Other government program (1997 forward)

• Single Service Plan (e.g., dental, vision, prescriptions) (1999 forward)

• No coverage of any type (2000 forward)

In 2004 and the first two quarters of 2005, only persons who did not answer "Single Service Plan" when asked about insurance coverage (HISINGLE) were asked the probe question about having additional single service coverage. However, beginning in quarter 3 of 2005, persons who reported single service plans in the initially health insurance coverage question were automatically assigned as responding "yes" to SSPROB. To increase consistency over time, IPUMS NHIS has recategorized persons who report having single service coverage (HISINGLE) in the initial health insurance question, as responding "yes" to SSPROB in 2004 and first two quarters of 2005. Additionally, in all years, IPUMS NHIS has recategorized the limited number of "unknown-not ascertained" responses to HISINGLE as also being "unknown-not ascertained" in SSPROB, rather than categorizing them as out of universe.