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Author: Admin | 2025-04-28
Between patent expiration and drug prices dynamics. We estimated 1 model per country, independently. The main assumption for our empirical strategy was that if drugs did not experience patent loss, their prices would have evolved in parallel to those under patent protection. Under this assumption, our model would adjust for constant price differences across drugs and common national pricing trends. To provide empirical support for this assumption, we estimated a dynamic version of an event study to examine the existence of pretrends with the Callaway and Sant’Anna difference-in-differences estimator.17 Another reason to use the estimator instead of a standard 2-way fixed-effects model was that if the treatment effects were heterogeneous across time, the standard difference-in-differences estimator would be inconsistent. The target estimate was the average treatment effect on the treated group (ATT), ie, the drug price changes associated with losing patent for those drugs whose patent expired. We clustered the standard errors of the coefficients of interest at the molecule level. To assess the degree of potential bias due to measurement error (difference between list prices and unobserved net prices), we performed a sensitivity analysis controlling for time-varying volume of sales. Statistical tests were 2-tailed and P Theoretical Cost-Effectiveness Modeling and Simulation Models To assess the influence of price dynamics after patent expiration on cost-effectiveness estimates, we created a simulation model focusing on 2 scenarios. In the first scenario, the originator drug was subject to patent protection for a time period before patent expiration, while the comparator drug was a generic. This first scenario, which assumed a constant price for the comparator, could also be interpreted as a drug vs nondrug comparative analysis. In the second scenario, both drugs—the originator and the comparator drug—were under patent protection, with the latter losing patent protection before the originator drug. For both scenarios, the outcome of interest was the difference in incremental cost-effectiveness ratios (ICERs) between the case where prices are allowed to change over time vs the case where prices are assumed to be constant. The motivation for our modeling approach was due to most economic evaluations of drugs occurring when a
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