Methods Matter:Investigating Causation &

Correlation

Are Local Health Department Expenditures Related to Racial

Disparities in Mortality?

David GrembowskiUniversity of Washington

Funded by the Robert Wood Johnson Foundation &Changes in Health Care Financing and Organization

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

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?

Apply a Conceptual Model

Physical & SocialEnvironment

Behavior

Human Biology

PopulationHealth &Disparities

Medical Care

Public Health

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

Choose a Study Design: Internal Validity

Longitudinal (randomized) experiment

Longitudinal observational data

Cross-sectional observational data

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)

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

Measure Mortality Disparities

Population Health Paradox

Population health has increased in many developed countries

Disparities in population health have increased in many developed countries

Absolute Change vs. Relative Disparity

in Infant Mortality by Racial/Ethnic Group

2002- Absolute 1950 2004 Change

Black 44 14 30 White 27 6 21 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

1997-1990 Absolute Change in All-Cause

Black Mortality Rates in Local Areas

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

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

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

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 rateLHD$: Local health department spending per capita

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))

Deal with Reverse Causation

Physical & SocialEnvironment

Behavior

Human Biology

PopulationHealth &Disparities

Medical Care

Public Health Spending

InstrumentalVariable

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

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

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

Assess External Validity

Mortality Rates & 1990/1997 Profile Surveys

Areas Areas with without 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___________________________________________________________________________________

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

Are Local Health Department Expenditures Related to Racial

Disparities in Mortality?

David GrembowskiDouglas ConradBetty BekemeierWilliam Kreuter

Eric Darst

University of Washington

Funded by the Robert Wood Johnson Foundation &Changes in Health Care Financing and Organization