Value of Medication Adherence in Chronic Vascular Disease: Fixed Effects Models of Health Services Utilization and Cost
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©2008 Caremark. All rights reserved. This presentation contains confidential and proprietary information of Caremark and cannot be reproduced, distributed or printed without written permission from Caremark.©2008 Caremark. All rights reserved. This presentation contains confidential and proprietary information of Caremark and cannot be reproduced, distributed or printed without written permission from Caremark.
Value of Medication Adherence in Chronic Vascular Disease: Fixed Effects Models of Health Services Utilization and Cost
M. Christopher Roebuck Director, Health Economics
Co-Authors: Liberman, J.; Gemmill-Toyama, M.; Brennan, T.
American Society of Health Economists3rd Biennial ConferenceCornell University, Ithaca, NYMonday, June 21, 20108:30-10:00am (Hollister 306)
©2008 Caremark. All rights reserved. Caremark proprietary and confidential information. Not for distribution.2
Background• Almost half of all Americans (approximately 133 million) suffer from at least
one chronic condition1
• Although medication adherence enhances health and reduces adverse health events, average compliance rates are just 50%2
• Because medication adherence increases pharmacy expenditures, payers and policymakers are interested in knowing whether lower medical costs from adherence offset these higher pharmacy costs
• If so, policies and programs to encourage medication adherence (e.g., value-based insurance design) may be well-worth their investment
• Despite the critical importance of estimating the value of medication adherence, the existing literature is surprisingly scant and methodologically challenged
1Centers for Disease Control and Prevention (CDC). Chronic disease overview [CDC website]. November 20, 2008. Available at: http://www.cdc.gov/NCCdphp/overview.htm. Accessed September 29, 2009.
2World Health Organization (WHO). Adherence to long-term therapies: evidence for action [World Health Organization website]. 2003. Available at: http://www.who.int/chp/knowledge/publications/adherence_report/en/index.html. Accessed September 29, 2009.
©2008 Caremark. All rights reserved. Caremark proprietary and confidential information. Not for distribution.3
Objectives
• To estimate the impact of medication adherence in four chronic vascular conditions (congestive heart failure (CHF), hypertension, diabetes, and dyslipidemia) on health services utilization and cost
• To examine whether adherence effects are different for seniors or by gender
©2008 Caremark. All rights reserved. Caremark proprietary and confidential information. Not for distribution.4
Literature: Main Findings• Clinical trials routinely document drug cost-effectiveness usually via reduced
hospitalizations and emergency room (ER) visits, however, results may not be applicable to “real world” treatment settings
– Controlled environment likely different than eventual community-based settings– Provide treatment versus non-treatment and dose-response effect estimates– Individuals aren’t randomized to adherent versus non-adherent cohorts– Observational data more readily available and allows for hypothetical treatments
• Observational studies generally find higher adherence associated with– Increased pharmacy costs– Usually increased outpatient visits – Often lower ER use and hospitalization– But its impact on total healthcare costs is not always a net benefit
• Sokol et al. (2005) report non-seniors have total healthcare cost savings from adherence to CHF, diabetes, dyslipidemia, and hypertension drugs
©2008 Caremark. All rights reserved. Caremark proprietary and confidential information. Not for distribution.
Literature: Challenges• Potential endogeneity of adherence
– Findings from observational studies are questionable since unobserved characteristics may be the real cause, thereby leading to biased estimates
– Adherent individuals may engage in other healthy behaviors such as regular exercise that are unmeasured and correlated with health services utilization and cost (i.e., the “healthy user” effect)
• Cross sectional studies do not allow one to determine the direction of causality (i.e., individuals may become adherent as a result of an adverse medical event)
• It is also difficult to determine the timing and duration of adherence effects
5
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Data• Integrated pharmacy and medical claims data on 135,008 patients from 9
employers• Annual panel dataset of individuals (age ≥ 18) with continuous eligibility
throughout study period: 7/1/05–6/30/08 (i.e., 3 observations per individual)• With one or more of the following diagnoses (ICD9CM):
– CHF: 428.x – Diabetes: 250.x – Dyslipidemia: 272.0, 272.2
– Hypertension: 401.x - 405.x • Final sample sizes:
– CHF:16,353– Diabetes: 42,080– Dyslipidemia: 53,041– Hypertension: 112,757
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Measuring AdherenceGoals:• Create a single adherence measure for each condition based on the
commonly used Medication Possession Ratio (MPR)• Considered adherence distribution and functional form of expected effect
– Using continuous MPR may not be clinically appropriate due to non-linear effects (i.e., is a movement from 0.10 to 0.30 clinically the same as 0.60 to 0.80?)
– Relatively arbitrary threshold of 0.80 generally referred to as “adherent”• Account for primary non-compliance
Steps followed:• For each of three 1-year observations• Calculated MPR by therapeutic class (TC)• Rolled up to condition-level as MPR mean, weighted by TC days’ supply• Created dichotomous measures of “optimally adherent” where MPR≥ 0.80• Time period started as of condition diagnosis date (i.e., MPR=0 for
individuals without medication)
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MPR Histograms0
510
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nsity
0 .2 .4 .6 .8 1HFMPR
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2025
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nsity
0 .2 .4 .6 .8 1HPMPR
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nsity
0 .2 .4 .6 .8 1DIMPR
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nsity
0 .2 .4 .6 .8 1CHMPR
Congestive Heart Failure Hypertension
Diabetes Dyslipidemia
©2008 Caremark. All rights reserved. Caremark proprietary and confidential information. Not for distribution.
Exploring Functional Form ofMPR→Total Healthcare Costs
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0 .2 .4 .6 .8 1
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LOCPR of MPR on THCG for HF
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LOCPR of MPR on THCG for HP
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LOCPR of MPR on THCG for DI
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Lower/Upper Limits of CILocal est.
LOCPR of MPR on THCG for CH
©2008 Caremark. All rights reserved. Caremark proprietary and confidential information. Not for distribution.10
VariablesDependent variables• Health services utilization:
– Annual inpatient hospital days– Annual emergency department visits– Annual outpatient physician visits
• Health services costs:– Annual gross pharmacy costs– Annual gross medical costs– Annual gross total healthcare costs
Independent variables– Optimally adherent– Charlson Comorbidity Index– Gender– Senior (≥65)– Vector of annual time dummies
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Methods
• We estimated 6 linear fixed effects models
• Included adherent main effect and interaction terms for male*adherent and senior*adherent in the models
• Used Driscoll & Kray heteroskedasticity-robust standard errors
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Sample MeansVariable CHF Hypertension Diabetes Dyslipidemia
Male 0.550 0.487 0.532 0.502
Age 77.301 68.401 67.872 65.096
Senior (Age ≥ 65) 0.872 0.614 0.615 0.517
Charlson Comorbidity Index 2.025 1.112 1.696 1.001
Annual Inpatient Hospital Days 11.901 3.291 4.255 2.239
Annual Emergency Dept Visits 0.613 0.318 0.353 0.265
Annual Outpatient Physician Visits 11.651 8.506 9.407 8.660
Annual Pharmacy Costs $3,780 $2,867 $3,624 $2,920
Annual Medical Costs $39,076 $14,813 $17,955 $12,688
Annual Total Healthcare Costs $42,856 $17,680 $21,580 $15,608
Medication Possession Ratio (MPR) 0.400 0.591 0.513 0.522
Optimally Adherent (MPR ≥ 0.80) 0.340 0.505 0.412 0.426
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Bivariate Results: Health Services Utilization and Cost by Medication Adherence StatusCondition
Adherence
Status
Inpatient Hospital
Days
Emergency Department
Visits
Outpatient Physician
Visits
Pharmacy Costs
Medical Costs
Total Healthcare
Costs
CHF
Non-adherent 13.220 0.648 11.344 $3,274 $42,549 $45,823
Adherent 8.046 0.569 14.339 $4,649 $33,113 $37,762
Hypertension
Non-adherent 4.245 0.372 8.690 $2,171 $16,835 $19,006
Adherent 1.613 0.256 8.708 $3,251 $11,041 $14,292
Diabetes
Non-adherent 4.695 0.372 9.236 $2,615 $18,501 $21,116
Adherent 2.520 0.313 10.228 $4,586 $14,725 $19,311
Dyslipidemia
Non-adherent 2.055 0.258 8.137 $1,932 $10,880 $12,812
Adherent 1.621 0.248 9.616 $3,850 $12,479 $16,329
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Fixed Effects Results: Impatient Hospital Days
Table 4. Estimated Effects of Medication Adherence on Annual Health Services Utilization by Chronic Vascular Condition
Health Services Utilization CategoryAdherence Comparison
Congestive Heart Failure(n = 16,353)
Hypertension(n = 112,757)
Diabetes(n = 42,080)
Dyslipidemia(n = 53,041)
Annual inpatient hospital days
Adherent (vs. non-adherent)-5.715*** -2.135*** -2.394*** -1.177***
Adherent female (vs. non-adherent female)-6.461*** -2.218*** -2.376*** -1.145***
Adherent male (vs. non-adherent male)-5.114*** -2.046*** -2.410*** -1.209***
Adherent senior (vs. non-adherent senior)-5.868*** -3.143*** -3.407*** -1.881***
Adherent non-senior (vs. non-adherent non-senior)-4.737*** -0.572*** -0.834*** -0.442***
Notes: Presented are marginal effect estimates from linear fixed effects models of health services utilization. All models included a weighted Charlson Comorbidity Index; two year indicator variables; dummy variables for senior, male, and adherent; and interaction terms for adherent with male and senior. Statistical significance based on robust Driscoll-Kraay standard errors denoted as follows: *** p<0.01; ** p<0.05; * p<0.10.
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Fixed Effects Results: Total Healthcare Costs
Table 5. Estimated Effects of Medication Adherence on Annual Health Services Costs by Chronic Vascular Condition
Health Services Cost CategoryAdherence Comparison
Congestive Heart Failure(n = 16,353)
Hypertension(n = 112,757)
Diabetes(n = 42,080)
Dyslipidemia(n = 53,041)
Annual total healthcare costs
Adherent (vs. non-adherent) -$7,823*** -$3,908*** -$3,756*** -$1,258***
Adherent female (vs. non-adherent female) -$11,506*** -$3,797*** -$3,335*** -$1,213***
Adherent male (vs. non-adherent male) -$4,860*** -$4,026*** -$4,126*** -$1,303***
Adherent senior (vs. non-adherent senior) -$7,893*** -$5,824*** -$5,170*** -$1,847***
Adherent non-senior (vs. non-adherent non-senior) -$7,374*** -$939*** -$1,576*** -$644***
Notes: Presented are marginal effect estimates from linear fixed effects models of health services utilization. All models included a weighted Charlson Comorbidity Index; two year indicator variables; dummy variables for senior, male, and adherent; and interaction terms for adherent with male and senior. Statistical significance based on robust Driscoll-Kraay standard errors denoted as follows: *** p<0.01; ** p<0.05; * p<0.10.
©2008 Caremark. All rights reserved. Caremark proprietary and confidential information. Not for distribution.
Discussion• Optimal medication adherence in CHF, hypertension, diabetes, and
dyslipidemia was associated with:– Increases in gross pharmacy costs and physician office visits– Decreases in emergency department visits and inpatient hospital days
• Higher pharmacy costs were more than offset by lower medical costs
• Average benefit-cost ratios were:– 8:1 for CHF– 10:1 for hypertension– 7:1 for diabetes– 3:1 for dyslipidemia– Highest was 13:1 for seniors with hypertension– Lowest was 2:1 for non-seniors with dyslipidemia
• Adherence effects are more pronounced for the elderly
• Adherence effects did not significantly differ by gender
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Limitations
• Endogeneity still possible– Reverse causality– Time-variant unobservables correlated with adherence and utilization/cost
• Difficult to determine the timing and duration of adherence effects
• Non-linear, two-part models perhaps more appropriate– Probit / negative binomial for count measures– Probit / gamma-log link GLM for cost data
• However, linear models have some advantages:– Fixed effects estimation is easier (e.g., fixed effects gamma/log GLM)– More easily explainable to medical journal readers (e.g., Health Affairs)
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Thank You!
• Comments and suggestions are welcomed
M. Christopher RoebuckCVS CaremarkDirector, Health Economics11311 McCormick Road, Suite 230Hunt Valley, MD 21031410-785-2136chris.roebuck@caremark.com
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