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Value Health. 2010 Sep-Oct;13(6):846-52. doi: 10.1111/j.1524-4733.2010.00730.x.

The impact of value-based benefit design on adherence to diabetes medications: a propensity score-weighted difference in difference evaluation.

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MedImpact Healthcare Systems, Inc, San Diego, CA 92131, USA.



To evaluate the impact of value-based benefit design (VBBD) on adherence to diabetes medications.


Health Alliance Medical Plans piloted VBBD for diabetes medications for a subgroup of 5400 enrollees in January 2007 while keeping drug benefits unchanged for the remaining plan enrollees. A difference in difference method (DID) was used to evaluate the effect of VBBD based on pharmacy claim data. Patients with unchanged benefits in the same plan were used as the control group. Adherence was measured by the proportion of days covered. Propensity score weighting was used to balance characteristics of the case group and the control group.


There were 71 patients in the case group and 5037 patients in the control group. The patients in the two groups had comparable characteristics after propensity score weighting. After the implementation of VBBD, the average copayment per 30 days of supply for diabetes medications decreased from $15.3 to $10.1 for the case group and increased from $14.6 to $15.1 for the control group. The probability of being adherent increased from 75.3% to 82.6% for the case group and was roughly unchanged from 79.1% to 78.5% for the control group. Propensity score-weighted DID analysis showed that patients with copayment reduction had greater odds of being adherent: odds ratio=1.56, P=0.03, 95% confidence interval 1.04-2.34.


A VBBD program that reduced the copayment for diabetes medications by 36.1% reduced the number of nonadherent patients by 30.0%.

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