Decomposing Gender Differences in Low
Density Lipoprotein Cholesterol
Among Veterans with or at Risk for
Cardiovascular Illness
Usha Sambamoorthi, PhD
Sopie Mitra, PhD
Ranjana Banerjea, PhD.
Leonard Pogach, MD,MBA.
University of Massachusetts Medical School
HSR&D Center for Healthcare Knowledge Management
Fordham University
Funded by VA HSR&D IEA-05-255; IIR-05-016
AcademyHealth
June 2009
Background
 Gender
differences in cardiovascular care is well
established
 Widest
gap observed in low density lipoprotein cholesterol
(LDL-C) control (i.e. lipid control)
 Women
were more likely to have poor lipid control
compared to men
 Most
studies focus on single disease framework
(examples)
 Diabetes
 Heart
Disease
Background
 Multi-morbidity
(the concurrent presence of two
or more chronic conditions) is receiving greater
attention
 Highly
prevalent, expensive, no evidence-based
clinical guidelines, complexities due to competing
demands
 Multi-morbidity
 similar
 more
with concordant conditions
pathophysiologic risk profile
likely to benefit from the same disease management
strategies
Objectives
 Examine
gender differences in poor lipid control
among individuals with multi-morbidity (i.e.
concordant conditions - any of the following
conditions)



Diabetes
Heart disease
Hypertension
 Examine
variations in these rates by demographic,
socio-economic, and health status predictors using
decomposition techniques
Study Population
 Multi-morbidity
(the concurrent presence of two
or more chronic conditions) is receiving greater
attention
 Highly
prevalent, expensive, no evidence-based
clinical guidelines, complexities due to competing
demands
 Multi-morbidity
 similar
 more
with concordant conditions
pathophysiologic risk profile
likely to benefit from the same disease management
strategies
How do we identify
CAD, DM, and HTN?
 Identification
of Diabetes, Heart Disease, and
Hypertension with ICD-9-CM codes
 Type
of healthcare encounters
 Inpatient
and outpatient
 Algorithms
1) Any one encounter with ICD-9-CM codes
2) At least one inpatient visit or one outpatient visit with
primary diagnosis or two outpatient visits without primary
diagnosis
What are the ICD-9-CM
codes?
Diabetes
'25000', '25001' ,'7902', '79021', '79022' ,'79029',
'7915' ,'7916', 'V4585', 'V5391', 'V6546','250'
Hypertension
'401','402','403','404','405','4372','642'
Heart disease
'410', '4110','4111','4118', ,'412','413', '414'
VA Data Center Austin
We use merged VHA and Medicare data
DSS
Lab
Data
Inpatient
Data
PBM
Pharmacy
Data
Medicare
Claims
(I,O)
Outpatient
Data
Veteran Status
VHA USER
Medicare
Eligibility
Merge
clean
Identify Cohorts
CAD
1 inp or
1 otp
prim
dx
or
2 otp
DM
1 inp or
1 otp
prim
dx
or
2 otp
HTN
1 inp or
1 otp
prim
dx
or
2 otp
WOMEN 23,437
Men: 828,429
Analytic Dataset
Study Population
 Veterans
using Veteran Health Administration
Clinic in Fiscal year 2002 (October 1, 2001 –
September 30, 2002).
 Diagnosed
with one of the following conditions
in FY 2002
 Diabetes
 Heart
Disease
 Hypertension
Analytic Dataset:
Inclusion Criteria
 Used
VHA clinics in 2002 and 2003
 Alive
as of the end of fiscal year 2003
 If
enrolled in Medicare, no HMO enrollment
 Had
a lipid test and lipid values recorded at the
VHA clinics in FY 2003
 23,437
women veterans
 828,429
men veterans
How do we define lipid control?
 Low
density lipoprotein cholesterol (LDL-C) from
the last recorded value in FY 2003
 Poor
 Not
control = LDL-C > 130 mg/dl
poor control = LDL-C <= 130 mg/dl
Independent Variables










Race/Ethnicity
Age
Marital Status
Metro
Region
VHA priority status
Medicare Enrollment
Lipid lowering therapy
Substance Use Disorders
Tobacco use



Depression
Other mental illness
Type of Chronic illness








Diabetes only
Heart Disease only
Hypertension only
Diabetes and Heart Disease
Diabetes and Hypertension
Heart Disease and
Hypertension
Diabetes, Heart Disease and
Hypertension
Other physical conditions
Statistical techniques


Unadjusted gender differences in poor lipid
control were examined using chi-square
tests
Multivariate analysis



Separate logistic regressions on poor lipid
control (women and men)
Quantile regressions on LDL-C values
Decomposition technique to estimate the
contribution of subject characteristics on lipid
control
Decomposition Technique
Y m −Y
f
 N m F ( X im βˆ m ) N f F ( X i f βˆ m )   N f F ( X i f βˆ m ) N f F ( X i f βˆ f ) 
= ∑
−∑
−∑
 + ∑

m
f
f
f
N
N
N
N
i =1
i =1
 i =1
  i =1

The first component is the “explained portion” of the LDL-C
control gap and represents the gap that is due to group differences in
observed distributions of X. The second component is the
“unexplained portion” of the gap, which is due to differences in the
estimated coefficients of the logistic equation, and to differences in
unobserved characteristics. The unexplained part may be understood
as physiological/genetic or other unobserved differences across
gender.
Decomposition Technique
Index Number Problem
Y
m
−Y
f
 N m F ( X im βˆ f ) N f F ( X i f βˆ f )   N m F ( X im βˆ m ) N m F ( X im βˆ f ) 
= ∑
−∑
−∑
 + ∑

m
f
m
N
N
N
Nm
i =1
i =1
 i =1
  i =1

an alternative to equation (1) would be to use women’s coefficient
estimates as weights for the first term and distributions of the
independent variables from men as weights for the second term as
shown in equation above.
Solution: Use co-efficient estimates from a pooled logistic
regression of men and women to represent a situation of gender
parity.
We provide a range of estimates for the explained
Pooled; Women and Men weights
Age
Distribution
Women
and
Men
Veterans
50%
40%
32%
38%
33%
30%
30%
23%
22%
20%
13%
10%
9%
0%
< 50
50 -64
65-74
75, +
DM, HRT, HTN Combinations
50%
38%
40%
38%
30%
28%
20%
12%
10%
9%
7%
6%
6%
3%
0%
DM only
HRT only
HTN only
Any Two
All three
Depression and Anxiety
50%
40%
30%
20%
29%
15%
17%
12%
10%
0%
Depression
Anx/PTSD
Lipid Lowering Drugs Use
60%
50%
54.9%
43.1%
40%
30%
Women
20%
MEN
10%
0%
Statin Use
Gender Gap in Poor Lipid Control:
11.5 percentage points
50%
40%
33.6%
30%
22.1%
20%
Women
MEN
10%
0%
Lipid Control
In pooled logistic regression women
compared to men were more likely to have
poor lipid control
1.60
Adjusted Odds Ratios
1.50
1.40
Poor Lipid Control
1.15
1.30
Women
1.37
1.37
1.09
0.98
1.20
1.10
lower bound
upper boun
custom +
custom -
1.33
1.41
0.04
0.04
1.00
1
Gender
[1.05,1.26]
[0.82,1.44]
[0.71,1.34]
**
1.12
1.06
0.85
[0.96,1.31]
[0.66,1.70]
[0.48,1.50]
Adjusted Odds Ratios and 95% Confidence Interval
Logistic Regression on Poor Lipid Control in Fiscal Year 2003 by Gender
Veteran Clinic Users with Diabetes, Heart Disease and Hypertension
Women
AOR
95% CI
Men
Sig
AOR
95% CI
Sig
DM, HEART, HTN
DM only
0.66
[0.60,0.73]
***
0.64 [0.63 , 0.66] ***
CAD only
0.75
[0.64,0.87]
***
0.68 [0.66 , 0.69] ***
DM CAD
0.63
[0.46,0.88]
**
0.48 [0.46 , 0.51] ***
DM HTN
0.59
[0.55,0.64]
***
0.55 [0.55 , 0.56] ***
CAD HTN
0.68
[0.62,0.75]
***
0.56 [0.55 , 0.57] ***
DM, CAD,
HTN
0.55
[0.48,0.63]
***
0.43 [0.42 , 0.44] ***
HTN only
ADJUSTED ODDS RATIOS
Percent Women with Poor Lipi
0.221
Percent Men with Poor Lipid C
0.336
Raw Gender Gap in Lipid Cont
-0.115
Pooled WeigWomen Wt Men Weigh
Decomposition
Unexplained
Explained (Total):
Predictors of Lipid Control
Race/Ethnicity
Age
Marital Status
Metro
Region
VHA Priority Status
Supplemental Insurance (M
Combinations of DM, CVD
Other physicial Illnesses
Depression
Serious Mental Illness
Anxiety and PTSD
Drug and/or Alcohol Use
Tobacco
Lipid Lowering Drug Use
54.8%
45.2%
67.0%
33.0%
53.0%
47.0%
1.9%
15.0%
1.6%
-0.8%
-0.2%
-0.1%
1.6%
17.0%
1.1%
1.7%
-0.2%
1.0%
0.3%
0.0%
5.5%
0.6%
6.9%
6.6%
0.1%
-1.1%
-1.2%
-1.3%
15.1%
0.7%
2.8%
-0.6%
0.7%
0.9%
0.0%
2.9%
1.9%
16.1%
1.3%
-0.8%
-0.2%
-0.1%
1.8%
17.2%
1.2%
1.7%
-0.2%
1.0%
0.3%
0.0%
5.7%
Sensitivity analyses
 Controlling
 Restricting
for selection bias
to veterans with lipid testing and
recorded values may be a biased study population
 Selection bias model (heckprob) with distance to
VA as the identifying variable, did not support
selection bias
 Quantile regressions suggested at all points in the
distribution (.10, .25, .50, .75, .90) women had
higher cholesterol values compared to men veterans
Conclusions
 Women
were more likely to have poor lipid
control
 Close to 50% of the gender gap was explained by
variables included in the model
 The major contributors were
 Age
 Combinations
of DM, Heart Disease and Hypertension
 Lipid lowering drugs use
 Depression
 Anxiety and PTSD
Implications



Interventions that improve lipid control among young
adults may reduce the gender gap
Aggressive management of lipid levels among women
with hypertension is needed
Controversy exists regarding statin use in women



Women were less likely to be on statins
Prescribing statins after personalized risk assessment may help
reduce the gap
Has implications for depression monitoring/treatment



Depression is positively related to poor lipid control
Past studies have found depression treatment is ineffective in
individuals with high cholesterol
Our findings suggest that treatment for depression needs to focus
on cholesterol management as well
Q&A