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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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
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Are local health department expenditures
related to racial disparities in mortality?
- or -
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What is the effect of local health
department expenditures on racial
disparities in mortality?
Apply a Conceptual Model
Physical & Social
Environment
Behavior
Human
Biology
Medical Care
Public Health
Population
Health &
Disparities
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
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LHD expenditures
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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
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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
1950
44
27
Black
White
B/W Rate
Ratio*
1.63
20022004
14
6
Absolute
Change
30
21
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 & Unobserved
Control 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 Differences
in 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
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 & Social
Environment
Behavior
Human
Biology
Medical Care
Public Health Spending
Instrumental
Variable
Population
Health &
Disparities
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
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1997-1990 Longitudinal Change in Mortality
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Endogeneity tests mostly not significant
No IV identified for 1997-1990 changes in health
department spending
Data Analysis & Results
 General Estimating Equations (GEE)
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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
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Per capita LHD expenditures generally
not related to disparities in all-cause, allage 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
with
Profile
Surveys
Both Yrs
1997-1990 Absolute Change
Black mortality
-83
White mortality
-41
Black infant mortality
White infant mortality
-3.0
-1.5
Areas
without
Profile
Surveys
Both Yrs
p-value
-34
-40
.004
.868
-1.8
-1.2
.070
.060
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Limitations
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Study design
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Omitted variables (e.g., population-level smoking, medical care rates)
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No data for LHDs without Profile Surveys
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No data for how LHDs spent funds in 1990/97 Profile Surveys
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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)
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Only 2 racial/ethnic groups
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