Bracketing in the comparative interrupted time-series design to address concerns about history interacting with group: Evaluating missouri handgun purchaser law

Raiden B. Hasegawa, Daniel W. Webster, Dylan S. Small

Research output: Contribution to journalArticlepeer-review

Abstract

In the comparative interrupted time series design (also called the method of differencein- differences), the change in outcome in a group exposed to treatment in the periods before and after the exposure is compared to the change in outcome in a control group not exposed to treatment in either period. The standard difference-in-difference estimator for a comparative interrupted time series design will be biased for estimating the causal effect of the treatment if there is an interaction between history in the after period and the groups; for example, there is a historical event besides the start of the treatment in the after period that benefits the treated group more than the control group. We present a bracketing method for bounding the effect of an interaction between history and the groups that arises from a time-invariant unmeasured confounder having a different effect in the after period than the before period. The method is applied to a study of the effect of the repeal of Missouri's permit-to-purchase handgun law on its firearm homicide rate. We estimate that the effect of the permit-to-purchase repeal on Missouri's firearm homicide rate is bracketed between 0.9 and 1.3 homicides per 100,000 people, corresponding to a percentage increase of 17% to 27% (95% confidence interval: [0.6,1.7] or [11%,35%]). A placebo study provides additional support for the hypothesis that the repeal has a causal effect of increasing the rate of state-wide firearm homicides.

Original languageEnglish (US)
JournalUnknown Journal
StatePublished - Apr 25 2019

Keywords

  • Bracketing
  • Causal inference
  • Comparative interrupted time series
  • Difference-in-difference
  • Firearm policy
  • Gun violence
  • History-by-group interaction
  • Multiple control groups
  • Permit-to-purchase
  • Unmeasured confounding

ASJC Scopus subject areas

  • General

Fingerprint Dive into the research topics of 'Bracketing in the comparative interrupted time-series design to address concerns about history interacting with group: Evaluating missouri handgun purchaser law'. Together they form a unique fingerprint.

Cite this