title: School shootings during 2013-2015 in the USA.
abstract: Data on the factors associated with school shootings in the USA are limited. The public conversation has often suggested several factors that may be linked to these events, however with little empirical support. Aiming to fill this gap, we describe the characteristics of school shooting incidents in the USA between 2013 and 2015 and explore whether four factors that represent domains of firearm policy, educational policy and epidemiological risk factors for intentional firearm injuries-background check (BC) policies, per capita mental health expenditures (MHE), K-12 education expenditure (KEE) and urbanicity-were associated with school shootings during this period.
  
  
  
  We searched LexisNexis, a newspaper and broadcast media databases for school shooting incidents from 1 January 2013 to 31 December 2015. Presence of BC laws was extracted from legal information in LexisNexis. State-level covariates of per capita MHE (2013), KEE (2013) and urbanicity (2010) rates were obtained from publicly available data sources. We used negative binomial regression models accounting for clustering by state to explore unadjusted associations between the BC laws, state-level covariates and school shootings to report IRR and 95% CI.
  
  
  
  We documented 154 school shootings (35, 55 and 64 each year). In unadjusted models, BC for firearm purchase (IRR=0.55, 95% CI 0.39 to 0.76), ammunition purchase (IRR=0.11, 95% CI 0.05 to 0.27), log per capita MHE (IRR=0.58, 95% CI 0.37 to 0.90), log per-capita KEE (IRR=0.09, 9% CI 0.02 to 0.29) and urbanicity (IRR=0.97, 95% CI 0.96 to 0.99) were associated with school shooting.
  
  
  
  School shootings are less likely in states with BC laws, higher MHE and KEE, and with greater per cent urban population.
authors.affiliation: Center for Translational Epidemiology and Comparative Effectiveness Research, Boston University, Boston, Massachusetts, USA.
authors.forename: Bindu
authors.identifier: 0000-0002-6543-2774
authors.initials: B
authors.lastname: Kalesan
authors.affiliation: Department of Epidemiology, Columbia University, New York, New York, USA.
authors.forename: Kinan
authors.initials: K
authors.lastname: Lagast
authors.affiliation: University of Texas Southwestern School of Medicine, Dallas, Texas, USA.
authors.forename: Marcos
authors.initials: M
authors.lastname: Villarreal
authors.affiliation: Department of Medicine, Boston University, Boston, Massachusetts, USA.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Pino
authors.affiliation: Department of Epidemiology, Columbia University, New York, New York, USA.|Columbia Law School, New York, New York, USA.
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Fagan
authors.affiliation: School of Public Health, Boston University, Boston, Massachusetts, USA.
authors.forename: Sandro
authors.initials: S
authors.lastname: Galea
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D002648:Child; D005260:Female; D005389:Firearms / Q000331:legislation & jurisprudence; D006708:Homicide / Q000706:statistics & numerical data*; D006801:Humans; D015994:Incidence; D008297:Male; D054527:Mass Casualty Incidents / Q000706:statistics & numerical data*; D010067:Ownership / Q000331:legislation & jurisprudence*; D011640:Public Policy; D012424:Rural Population; D012574:Schools / Q000331:legislation & jurisprudence; D012737:Sex Factors; D013405:Suicide / Q000706:statistics & numerical data*; D014481:United States / Q000453:epidemiology; D014505:Urban Population; D014948:Wounds, Gunshot / Q000453:epidemiology*; D055815:Young Adult