TABLE 4—
Effects of Gun Ownership Level on Age-Adjusted Firearm Homicide Rate: United States, 1981–2010
| Gun Ownership Level | IRR (95% CI) | P |
| Current gun ownership | ||
| Full modela | 1.008 (1.004, 1.012) | .001 |
| Excluding states with missing datab | 1.009 (1.005, 1.014) | .001 |
| Restricted to years 2001, 2002, and 2004c | 1.023 (1.014, 1.032) | .001 |
| Survey measure of gun ownership used instead of proxy measure (years 2001, 2002, and 2004 only)d | 1.016 (0.997, 1.036) | .1 |
| Full model executed in SASe | 1.009 (1.004, 1.014) | .001 |
| Variables with interpolated or extrapolated values omitted from analysisf | 1.009 (1.005, 1.014) | .001 |
| Control for temporal trends in homicide rates (linear and quadratic terms for time included in model) | 1.010 (1.005, 1.014) | .001 |
| Individual data points weighted by square root of state population | 1.011 (1.005, 1.017) | .001 |
| Poisson model instead of negative binomial model | 1.008 (1.004, 1.013) | .001 |
| Gun ownership in previous years | ||
| Lagged 1 y | 1.009 (1.005, 1.013) | .001 |
| Lagged 2 y | 1.005 (1.001, 1.009) | .024 |
Note. CI = confidence interval; IRR = incidence rate ratio.
Included fixed effects for year, adjustment for clustering within states, and controls for percentage young (aged 15–29 y), percentage young males, percentage Black, percentage Hispanic, poverty, unemployment, household income, educational attainment, income inequality, level of urbanization, alcohol consumption, violent crime rate, nonviolent crime rate, hate crime rate, divorce rate, hunting licenses, region, age-adjusted nonfirearm homicide rate, incarceration rate, and suicide rate.
Excluded data from states with missing data for age-adjusted firearm homicide rate in any year: New Hampshire, North Dakota, Vermont, Wyoming, Hawaii, and South Dakota.
Years for which Behavioral Risk Factor Surveillance System (BRFSS) data on household gun ownership were available.
Main predictor variable was proportion of households with guns according to BRFSS in 2001, 2002, and 2004; proxy measure (firearm suicides divided by all suicides) was not used in this model.
Model run with PROC GENMOD in SAS version 9.1 (SAS Institute, Cary, NC), with empirical SEs.
Variables with interpolated or extrapolated values were household income, educational attainment, income inequality, level of urbanization, hate crime rate, divorce rate, and incarceration rate.