Correcting for transitory effects in RCTs: Evidence from the RAND Health Insurance Experiment
研究发现兰德健康保险实验中存在显著的“截止日期效应”，即实验最后一年支出激增，且低共保率参与者支出增幅更大。剔除该效应后，药品支出的永久价格弹性估计值下降，意味着最优共保率应提高。
Abstract Temporary randomized controlled trials are susceptible to transitory effects that would not result from a permanent treatment. We find a large and statistically significant “deadline effect”—a surge in spending in the final treatment year—in the RAND Health Insurance Experiment, identified by random allocation to three‐ or five‐year enrolment terms. Participants facing lower coinsurance rates show larger spending surges. Partialing out the price–deadline interaction reduces in magnitude estimates of the permanent price elasticity of drug spending (and in some specifications of outpatient and supplies spending). This implies higher optimal coinsurance rates and illustrates the importance of experimental design to identifying parameters of interest in randomized controlled trials.