title: Constructing "behavioral" comparison groups: A difference-in-difference analysis of the effect of copayment based on the patient's price elasticity.
abstract: It is well known that the differences-in-differences (DD) estimator is based on the assumption that in the absence of treatment, the average outcomes for the treated group and the control group will follow a common trend over time. That can be problematic, especially when the selection for the treatment is influenced by the individual's unobserved behavior correlating with the medical utilization. The aim of this study was to develop an index for controlling a patient's unobserved heterogeneous response to reform, in order to improve the comparability of treatment assignment. This study showed that a DD estimator of the reform effects can be decomposed into effects induced by moral hazard and by changes in health risk within the same treated/untreated group. This article also presented evidence that the constructed index of the price elasticity of the adjusted clinical group has good statistical properties for identifying the impact of reform.
authors.affiliation: Department of Risk Management and Insurance, National Kaohsiung First University of Science and Technology, Kaohsiung, Taiwan linchao@nkfust.edu.tw.
authors.forename: Chaohsin
authors.initials: C
authors.lastname: Lin
authors.affiliation: Department of Risk Management and Insurance, National Kaohsiung First University of Science and Technology, Kaohsiung, Taiwan.
authors.forename: Shuofen
authors.initials: S
authors.lastname: Hsu
mesh_terms: D003627:Data Interpretation, Statistical; D003669:Deductibles and Coinsurance / Q000706:statistics & numerical data*; D005251:Fees, Medical / Q000706:statistics & numerical data*; D018166:Health Care Reform; D006291:Health Policy; D006801:Humans; D018803:Models, Economic; D012107:Research Design; D013624:Taiwan
keywords: adjusted clinical group (ACG); copayment reform; differences-in-differences (DD); identification; natural experiment