Measurement of Income in NCHS Surveys Diane M. Makuc NCHS Data Users Conference July 12, 2006 Centers for Disease Control and Prevention National Center for Health Statistics

Outline of Presentation Why collect income in health surveys? NCHS surveys with income data Measurement of income Data issues and limitations

Why collect income in health surveys? Income affects health and health care Monitor socioeconomic disparities in health Healthy People 2010 Congressionally mandated reports Evaluate health policies to improve health / health care for low income population

Income and Health Status Education Income Early life experiences Environment/ Living conditions Human biology/ genetics Health behaviors Health insurance/ Health care Psychological/ Psychosocial factors Health status

Year Percent of Persons with Untreated Dental Caries by Poverty Status Data Source: National Health and Nutrition Examination Survey <100% 100-<200% 200+% Ages 6-17 years < < Year Ages years

NCHS surveys that collect income data National Health Interview Survey (NHIS) National Health and Nutrition Examination Survey (NHANES) National Survey of Family Growth (NSFG)

NCHS surveys that collect income data State and Local Area Integrated Telephone Survey (SLAITS) National Survey of Early Childhood Health (NSECH) National Survey of Children with Special Health Care Needs (NSCSHCN) National Survey of Children’s Health (NSCH) National Asthma Survey (NAS)

Income and related data collected by NHIS, NHANES, NSFG Individual earnings amount – NHIS only Sources of family income - all For each family member - NHIS / NHANES Total family income amount - all Program participation - all For each family member - NHIS / NHANES Home ownership – NHIS only

Total family income amount questions: NHIS and NHANES Exact total combined family income amount in previous calendar year (NHIS) / last 12 months (NHANES) Followup questions for nonresponders to exact amount 2 categories ( $20,000) 44 categories ( $75,000)

Total family income amount questions: NSFG 14 categories of total combined family income ( $1442 in week or $6250 in month or $75000 in year) Followup questions for nonresponders to 14- category question 3 categories – questions depend on previous responses Is income $50,000?

Total family income amount questions: SLAITS Exact amount in previous calendar year for family (NSCH, NSECH) or for household (NSCSHCN, NAS) Followup questions for nonresponders 15 income categories - questions depend on previous responses e.g. Is income $7,500? 9 categories of poverty ratios - questions depend on previous responses (NSCH, NSCSHCN).

Income data collection method Computer assisted personal interview in household (CAPI) NHIS and NHANES Audio computer assisted self-administered interview (audio CASI) NSFG Computer assisted telephone interview (CATI) SLAITS - all 4

Income variables on public use files: % missing (unweighted) and number of income groups NHIS (2005)29% groups NHANES (2003-4) 6% groups NSFG (2002) 8% groups NAS (2003)23% groups NSCH (2003-4) 9% -- 8 groups NSCSHCN (2000-2)15% -- 9 groups NSECH (2000)11% -- 8 groups

Factors that may affect income nonresponse Data collection mode - Income question is self- administered in NSFG Survey content – NHANES respondents receive physical exams and lab tests Question wording – SLAITS uses “bracketed” questions for nonresponders to exact income Survey response rate - NHIS has higher survey response rate (86% in 2005) than other surveys

Imputation of family income amount NHIS - multiple imputation of missing income values Available on public use files about 3 months after initial file release NSFG – single imputation of missing income values NSCSHCN – single imputation of low income status for uninsured with missing income values

Data issues in analyzing income and health Surveys may exclude some of the lowest income persons who are likely to have health problems Household surveys exclude homeless and institutionalized Telephone surveys exclude those without any phone and those with only cell phones

Data issues in analyzing income and health Responses to health questions (particularly subjective health measures) may be influenced by income level. Income in a single year has limitations as a measure of financial resources It may underestimate the effect of income on health. For older people, wealth may be a more important measure of financial resources.

Summary Income data are difficult to collect resulting in high nonresponse in many surveys. Differences in income response among surveys indicate that improvements may be possible. Imputation of missing values may reduce bias associated with high nonresponse.

For more information See NCHS website //