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Methods Matter: Investigating Causation & Correlation

Methods Matter: Investigating Causation & Correlation. Are Local Health Department Expenditures Related to Racial Disparities in Mortality? David Grembowski University of Washington Funded by the Robert Wood Johnson Foundation & Changes in Health Care Financing and Organization. Outline.

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Methods Matter: Investigating Causation & Correlation

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  1. Methods Matter:Investigating Causation & Correlation Are Local Health Department Expenditures Related to Racial Disparities in Mortality? David Grembowski University of Washington Funded by the Robert Wood Johnson Foundation & Changes in Health Care Financing and Organization

  2. Outline • Write the question • Apply a conceptual model • Choose a study design • Identify data sources • Measure mortality disparities • Identify control variables in conceptual model • Link mortality & control variables • Adjust for baseline mortality differences • Address variation in covariates over time • Deal with reverse causation • Data analysis & results • Assess external validity • Limitations

  3. Write the Question • Are local health department expenditures related to racial disparities in mortality? - or - • What is the effect of local health department expenditures on racial disparities in mortality?

  4. Apply a Conceptual Model Physical & Social Environment Behavior PopulationHealth & Disparities Human Biology Medical Care Public Health

  5. Can Local Public Health Reduce Racial/Ethnic Disparities? • Yes! • Population-based interventions that influence everyone have the potential to reduce health disparities • Water fluoridation, highway safety improvements • Raising the health of the worst off fastest • No! • Population-based interventions that depend on voluntary participation may increase disparities because people with more resources are more likely to take advantage of them • Goal of improving population health may conflict with goal of reducing health disparities Link & Phelan 2005; Mechanic 2002

  6. Choose a Study Design: Internal Validity Longitudinal (randomized) experiment Longitudinal observational data Cross-sectional observational data

  7. Choose a Study Design Time-Trend Ecologic Study Design Test whether changes in LHD spending per capita are associated with changes in Black & White mortality rates (Temporal rather than causal effects)

  8. Identify Data Sources • LHD expenditures • 1990 & 1997 National Profiles of Local Health Departments from the National Association of County and City Health Officials (NACCHO) • 1990 & 1997 Black and White mortality rates from CDC • County Sociodemographic and Government Characteristics from U.S. Census & Area Resource File • County Medicare expenditures from Centers for Medicare and Medicaid Services • Rural/urban county commuting codes from Department of Agriculture

  9. Measure Mortality Disparities Population Health Paradox • Population health has increased in many developed countries • Disparities in population health have increased in many developed countries

  10. Absolute Change vs. Relative Disparityin Infant Mortality by Racial/Ethnic Group 2002- Absolute 19502004Change Black 44 14 30 White27 621 B/W Rate Ratio* 1.63 2.33 .70 bigger gap * 1950 Black/White Rate Ratio = 44/27 = 1.63 Infant mortality rate: rate of deaths in children less than 1 year old per 1,000 live births Health, United States, 2007

  11. 1997-1990 Absolute Change in All-Cause Black Mortality Rates in Local Areas

  12. 1997-1990 Change in Black/White Rate Ratios in Local Areas

  13. Identify Observed & UnobservedControl Variables in Conceptual Model Social Environment Biology Education Female Income Income inequality Physical Environment White collar occupation Rural/Urban Unemployment Household size Medical Care Single female household Medicare expenditures Percent Black Hospital beds Foreign residents Physicians English speaking Veterans Behavior Home values Drive to work People in mental institutions People in correctional institutions

  14. Link Mortality & Control Variables Black mortality = f(Black income per capita) White mortality = f(White income per capita) Black/White = f(Black/White income per capita) rate ratio

  15. Adjust for Baseline Differencesin Mortality BM97 – BM90 = f((LHD$97 – LHD$90) , Covariates) - or - BM97 – BM90 = f(BM90 , (LHD$97 – LHD$90) , Covariates) BM: Black mortality rate LHD$: Local health department spending per capita

  16. Address Time-Invariant & Time-Variant Covariates Time-Invariant Covariates (?) Smoking is Unobserved (no county data) WM = White mortality rate WM90 = f(Education90 , Smoking90) WM97 = f(Education90 , Smoking90) WM97 – WM90 = f((Education90 – Education90) , (Smoking90 - Smoking90)) Time-Variant Covariates (?) WM97 – WM90 = f((Education97 – Education90) , (Smoking97 - Smoking90))

  17. Deal with Reverse Causation Physical & Social Environment Behavior PopulationHealth & Disparities Human Biology Medical Care Public Health Spending Instrumental Variable

  18. Deal with Reverse Causation • 1990 Cross-Sectional Analyses • Endogeneity tests significant • Instrumental variables for 1990 LHD spending • County government revenue per capita • Average county home value • 1997-1990 Longitudinal Change in Mortality • Endogeneity tests mostly not significant • No IV identified for 1997-1990 changes in health department spending

  19. Data Analysis & Results • General Estimating Equations (GEE) • 40 binary (0,1) State variables to control for State-level influences on local areas • Standard errors adjusted for clustering of local areas by Federal Region • Hausman-Durbin-Wu test for 2-way causation between LHD spending and mortality

  20. Results • Per capita LHD expenditures generally not related to disparities in all-cause, all-age Black and White mortality rates and infant mortality rates • We also are analyzing whether LHD services are related to Black/White disparities in mortality

  21. Assess External Validity Mortality Rates & 1990/1997 Profile Surveys Areas Areas withwithout Profile Profile Surveys Surveys Both Yrs Both Yrs p-value 1997-1990 Absolute Change Black mortality -83 -34 .004 White mortality -41 -40 .868 Black infant mortality -3.0 -1.8 .070 White infant mortality -1.5 -1.2 .060 ___________________________________________________________________________________

  22. Limitations • Study design • Omitted variables (e.g., population-level smoking, medical care rates) • No data for LHDs without Profile Surveys • No data for how LHDs spent funds in 1990/97 Profile Surveys • No data for public health spending by other community agencies • Black county populations often too small to calculate cause of death mortality rates (by gender and by age group) • Only 2 racial/ethnic groups

  23. Are Local Health Department Expenditures Related to Racial Disparities in Mortality? David Grembowski Douglas Conrad Betty Bekemeier William Kreuter Eric Darst University of Washington Funded by the Robert Wood Johnson Foundation & Changes in Health Care Financing and Organization

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