Value of Medication Adherence in Chronic Vascular Disease: Fixed Effects Models of Health Services Utilization and Cost
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Value of Medication Adherence in Chronic Vascular Disease: Fixed Effects Models of Health Services Utilization and Cost

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  • Thursday, June 2, 2011
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Value of Medication Adherence in Chronic Vascular Disease: Fixed Effects Models of Health Services Utilization and Cost Value of Medication Adherence in Chronic Vascular Disease: Fixed Effects Models of Health Services Utilization and Cost Presentation Transcript

  • 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 Economists 3 rd Biennial Conference Cornell University, Ithaca, NY Monday, June 21, 2010 8:30-10:00am (Hollister 306)
  • Background
    • Almost half of all Americans (approximately 133 million) suffer from at least one chronic condition 1
    • 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
    • 1 Centers 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.
    • 2 World 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.
  • 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
  • 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
  • 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
  • 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
  • Measuring Adherence
    • Goals:
    • 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)
  • MPR Histograms Congestive Heart Failure Hypertension Diabetes Dyslipidemia
  • Exploring Functional Form of MPR->Total Healthcare Costs
  • Variables
    • Dependent 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
  • 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
  • Sample Means Variable 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
  • Bivariate Results: Health Services Utilization and Cost by Medication Adherence Status Condition 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
  • Fixed Effects Results: Impatient Hospital Days 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. Table 4. Estimated Effects of Medication Adherence on Annual Health Services Utilization by Chronic Vascular Condition Health Services Utilization Category Adherence 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***
  • Fixed Effects Results: Total Healthcare Costs 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. Table 5. Estimated Effects of Medication Adherence on Annual Health Services Costs by Chronic Vascular Condition Health Services Cost Category Adherence 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***
  • 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
  • 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)
  • Thank You!
    • Comments and suggestions are welcomed
        • M. Christopher Roebuck
        • CVS Caremark
        • Director, Health Economics
        • 11311 McCormick Road, Suite 230
        • Hunt Valley, MD 21031
        • 410-785-2136
        • [email_address]