Background Virtually all existing evidence linking access to firearms to elevated risks of mortality and morbidity comes from ecological and case–control studies. To improve understanding of the health risks and benefits of firearm ownership, we launched a cohort study: the Longitudinal Study of Handgun Ownership and Transfer (LongSHOT).
Methods Using probabilistic matching techniques we linked three sources of individual-level, state-wide data in California: official voter registration records, an archive of lawful handgun transactions and all-cause mortality data. There were nearly 28.8 million unique voter registrants, 5.5 million handgun transfers and 3.1 million deaths during the study period (18 October 2004 to 31 December 2016). The linkage relied on several identifying variables (first, middle and last names; date of birth; sex; residential address) that were available in all three data sets, deploying them in a series of bespoke algorithms.
Results Assembly of the LongSHOT cohort commenced in January 2016 and was completed in March 2019. Approximately three-quarters of matches identified were exact matches on all link variables. The cohort consists of 28.8 million adult residents of California followed for up to 12.2 years. A total of 1.2 million cohort members purchased at least one handgun during the study period, and 1.6 million died.
Conclusions Three steps taken early may be particularly useful in enhancing the efficiency of large-scale data linkage: thorough data cleaning; assessment of the suitability of off-the-shelf data linkage packages relative to bespoke coding; and careful consideration of the minimum sample size and matching precision needed to support rigorous investigation of the study questions.
- cohort study
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Contributors YZ, EEH, LP and DMS conducted all data cleaning. YZ, EEH and DMS developed and implemented the linkage algorithms. DMS obtained project funding, with assistance from YZ, GJW, JAR, MJM and SAS. DMS, YZ, GJW and LP obtained the study data. JR provided expert advice regarding voter registration data and geocoding. MJM, JAR, SAS and GJW advised on study design and helped troubleshoot issues arising in the data linkage. DS wrote the first draft of the manuscript. YZ, EEH, LP, JAR, SAS, MJM and GJW contributed revisions relating to important intellectual content. DMS is the guarantor of the study.
Funding The study was funded by the Fund for a Safer Future (Grant No GA004696) and the Joyce Foundation (Grant No 17-37241).
Competing interests None declared.
Patient consent for publication Not required.
Ethics approval The LongSHOT project was approved by the Institutional Review Board at Stanford University.
Provenance and peer review Not commissioned; externally peer reviewed.
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