Overview of the National Health Interview Survey

1. U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES Centers for Disease Control and Prevention National Center for Health Statistics Overview of the National Health Interview Survey Jane F. Gentleman, Ph.D.

2. NHIS Purpose • To collect data on the health status and health services utilization of the US population • To address specific issues of current public health concern

3. Uses of NHIS Data • “Snapshot” of health of the US population • Track national health objectives • Plan and evaluate health policies • Public health research

4. Roster of families and members Demographics Socioeconomic status Limitation of activity Injuries and poisonings Respondent assessment of health status Questionnaire Contents

5. Questionnaire Contents • Utilization of health care services • Health insurance status • Chronic conditions • Health behavior • Height and weight supplements

6. NHIS Sample Design • Household interview survey • Nationally and regionally representative of the non-institutionalized civilian population of the United States • Complex design • Over-sample black and Hispanic populations

7. NHIS Sample Design • Fielded continuously throughout year • Each week – representative sample • 1995-2006 design • ~40,000 households; ~105,000 persons • ~37,000 sample adults • ~15,000 sample children

8. NHIS Target Population • Excludes persons in: • The military • Long-term care facilities • Prison • Eligible for interview: • Group homes • Assisted living facilities • Campuses • Resident aliens

9. NHIS Field Procedures • Trained interviewers from the US Census Bureau • In-home personal interview • Use of telephone permitted after initial contact if necessary • Advance letter • Informed consent

10. NHIS Questionnaire Modules • Basic Module or Core • Fielded each year • Supplemental Modules • New topics or more detail on Core topics • Different each year

11. 1997 NHIS Redesign • Major changes in questionnaire content and format • Purpose of redesign: • Improve data quality and timeliness • More relevant data • Shorten interview • Implement a Computer Assisted Personal Interview (CAPI) instrument

12. Questionnaire Coverage Includes Component Household All HH members Family All family members Sample Child One child/family Immunization Sample child Sample Adult One adult/family Supplements Any of the above

13. NHIS Data Files Questionnaire Data Files Household Household file Family Family & Person File Sample Adult Sample Adult File Sample Child Sample Child File Immunization Child Immunization File Supplemental Separate File (or not)

14. Data for entire household (HH) Examples of Variables: Number of families/persons Month/year of Interview Telephone service NHIS Household File

15. Data for all families in HH Examples of variables: Characteristics of family housing unit Health-related variables: Does anyone in family… How many in family… Health insurance coverage NHIS Family File

16. Data for each person in all families Examples of variables Hispanic ethnicity, race, sex, age Limitation of activity (causal conditions) Access to care Utilization of health care services Birthplace and citizenship NHIS Person File

17. Data from one randomly selected adult per family Examples of variables: Chronic Conditions (main) Sad/nervous/hopeless etc. Work loss/sick days Health status compared to year ago Smoking Physical Activity Surgical procedures Sample Adult File

18. Data for a randomly selected child Similar data to sample adult except: Birth height/weight List of appropriate conditions Asthma/allergies Child mental health questions (vary by age) The section on immunizations is expanded Sample Child File

19. Selected NHIS Supplements 1998-2005 • 1998: Prevention/Healthy People 2000 • 1999: Mental health, conditions, utilization, Healthy People 2000 • 2000: Cancer Control • 2001: Healthy People 2010, Children’s mental health

20. Selected NHIS Supplements 1998-2005 • 2002: Healthy People 2010, Complementary and Alternative Medicine, Children’s mental health • 2003: Healthy People 2010, Children’s mental health, Cell phone usage • 2004: Children’s mental health, Cell phone usage • 2005: Cancer Control

21. Examples of Important Recoded Variables • Examples: • Health insurance coverage status as reported in Health, United States (NOTCOV) • Race ethnicity recode to comply with the OMB-15 data collection standard (RACERP_I) • Categorical description of family income (INCGRP)

22. Geographic Detail from NHIS • National • 4 Census Regions: NE, Midwest, South, West • MSA size • State, city, and county not identified on Public Use Files

23. Component Response Rates:Conditional Component 1999 2000 2001 2002 Percent Family 98 98 99 98 Sample child 91 91 92 92 Sample adult 81 83 84 84

24. Component Response Rates:Unconditional Component 1999 2000 2001 2002 Percent Family 86 87 88 88 Sample child 78 79 81 81 Sample adult 70 72 74 74

25. Integration of NHIS with Other Surveys • NHIS is periodically linked to the National Death Index • NHIS respondents serve as the sampling frame for the Medical Expenditure Panel Survey (MEPS) • NHIS and MEPS are periodically linked

26. NHIS Strengths • Large, representative sample • In-person survey • Broad range of information • Demographic detail • Ease of access: available free via Internet and CD-ROM

27. NHIS Strengths • Ongoing annual survey • Trends over time • Combine years to increase sample sizes • Topical supplementary information • Relatively high response rates • Links to NDI, MEPS

28. NHIS Limitations • For User: • Limited ability to make sub-national estimates • Complex to analyze • For NCHS • Cost in $$ and timeliness for in-person survey

29. Research Data Center • Provides a mechanism for researchers to access: • Data usually not released to the public because of nondisclosure or confidentiality reasons • Small area or micro data • NHIS data merged with other files • Each request is considered on a case-by-case basis

30. http://www.cdc.gov/nchs/nhis.htm Announcements Join the listserv Access data files Documentation for released files Questionnaires Publications NHIS Web Site

31. NHIS Early Release (ER) • Objective • Improve access to the most recent NHIS estimates • Monitor health and health care • Measure progress toward national public health objectives • NHIS ER: Features • Web-based only • Selected estimates based on full- or partial-year data • Release quarterly in Mar., June, Sept., and Dec. • Timely: 6 months after the end of data collection each quarter