. Author manuscript; available in PMC: 2015 Aug 7.

Published in final edited form as: Accid Anal Prev. 2012 Aug 11;50:778–786. doi: 10.1016/j.aap.2012.07.002

Table 3.

Incidence-rate ratios (IRR) and 95% confidence intervals (CI) for random effects negative binomial regression: reported injuries with lost workdays in the 5669 mine-year records used.

	IRR	Std. err.	p > z	[95% CI]
Ln real revenue per hour worked	0.886	0.013	0.000	0.862	0.912
Mine age	0.962	0.002	0.000	0.958	0.966
Union status (union = 1)	1.170	0.028	0.000	1.117	1.226
Mining method (longwall = 1)	0.907	0.035	0.011	0.841	0.978
Region
Central (reference)
North	1.014	0.047	0.768	0.925	1.111
Midwest	0.953	0.055	0.402	0.851	1.067
West	0.897	0.068	0.148	0.774	1.040
South	0.709	0.083	0.003	0.564	0.891
Total hours worked			(Exposure)
/ln_r	1.988	0.064		1.862	2.113
/ln_s	2.265	0.079		2.110	2.420
R	7.299	0.467		6.439	8.275
S	9.632	0.761		8.250	11.245
Number of observations			5669
Number of groups			1407
Obs. per group
Min			1
Max			17
Average			4
Wald χ² (8)			743.99
Log likelihood (prob > χ²)			−15,989 (0.000)
Pseudo R²			0.68