. 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 2.

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

	IRR	Std. err.	p > z	[95% CI]
Ln real revenue per hour worked	0.911	0.012	0.000	0.887	0.935
Mine age	0.966	0.002	0.000	0.963	0.970
Union status (union = 1)	1.126	0.025	0.000	1.079	1.175
Mining method (longwall = 1)	0.865	0.031	0.000	0.806	0.929
Region
Central (reference)
North	1.062	0.047	0.172	0.974	1.157
Midwest	0.963	0.053	0.489	0.865	1.072
West	0.942	0.066	0.399	0.821	1.082
South	0.471	0.050	0.000	0.382	0.579
Total hours worked			(Exposure)
/ln_r	1.851	0.061		1.732	1.970
/ln_s	2.452	0.076		2.304	2.601
R	6.368	0.386		5.655	7.172
S	11.612	0.880		10.010	13.471
Number of observations			5669
Number of groups			1407
Obs. per group
Min			1
Max			17
Average			4
Wald χ² (8)			739.89
Log likelihood (prob > χ²)			−17,820
Pseudo R²			0.56