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. 2019 Sep 20;19:1147. doi: 10.1186/s12889-019-7490-x

Table 4.

Multilevel Models: Incidence Rate Ratios of Mass Shootings in U.S. Counties

	MSA: Three or More Injuries		MSA: Four or More Deaths
	MS_2000–2009 = ∆ Covariates_1990–2000	MS_2010–2015 = ∆ Covariates_2000–2010	MS_2000–2009 = ∆ Covariates_1990–2000	MS_2010–2015 = ∆ Covariates_2000–2010
	Adj. IRR (95% CI)	Adj. IRR (95% CI)	Adj. IRR (95% CI)	Adj. IRR (95% CI)
Level 1 = County-Level
Income inequality	1.47 (1.06, 2.02)	1.50 (1.14, 1.97)	1.54 (1.12, 2.11)	1.63 (1.15, 2.33)
Poverty rate	0.76 (0.39, 1.47)	2.46 (1.50, 4.03)	0.59 (0.39, 0.90)	2.50 (1.06, 5.91)
Unemployment rate	0.83 (0.57, 1.22)	1.24 (0.90, 1.69)	0.96 (0.58, 1.59)	0.94 (0.49, 1.78)
Population density	0.26 (0.03, 2.05)	0.00 (0.00, 0.16)	0.16 (0.01, 1.71)	0.04 (0.00, 3.50)
Young population	0.74 (0.48, 1.13)	2.98 (1.65, 5.39)	0.83 (0.51, 1.34)	2.54 (1.36, 4.75)
Minority population	0.87 (0.07, 9.85)	6.58 (2.08, 20.80)	8.61 (1.07, 69.35)	10.43 (2.81, 38.67)
HS graduation rate	0.19 (0.06, 0.59)	0.99 (0.85, 1.16)	0.19 (0.03, 0.96)	1.00 (0.85, 1.18)
Level 2 = State-Level
Right to carry laws	4e⁻³² (3e⁻⁶⁵, 50.74)	1.05 (0.39, 2.86)	1e⁻³⁶ (9e⁻⁴⁰, 3e⁻³³)	0.40 (0.00, 48.93)
Assault rifle ban	1e⁻²⁹ (3e^− 32, 3e⁻²⁷)	0.84 (0.19, 3.64)	0.16 (0.00, 1972.26)	2.27 (0.95, 5.37)
Wald Chi-Square	20.17	86.93	22.48	63.22
County-Decades (N)	3134	3139	3134	3139

Adj. IRR adjusted incidence rate ratio, CI confidence interval. All variables are logged and z-score standardized