Matching and Regression to the Mean in Difference-in-Differences Analysis.

ABSTRACT:

Objective

To demonstrate regression to the mean bias introduced by matching on preperiod variables in difference-in-differences studies.

Data sources

Simulated data.

Study design

We performed a Monte Carlo simulation to estimate the effect of a placebo intervention on simulated longitudinal data for units in treatment and control groups using unmatched and matched difference-in-differences analyses. We varied the preperiod level and trend differences between the treatment and control groups, and the serial correlation of the matching variables. We assessed estimator bias as the mean absolute deviation of estimated program effects from the true value of zero.

Principal findings

When preperiod outcome level is correlated with treatment assignment, an unmatched an

SUBMITTER: Daw JR 

PROVIDER: S-EPMC6232412 | biostudies-literature | 2018 Dec

REPOSITORIES: biostudies-literature