. Author manuscript; available in PMC: 2014 Jul 23.

Published in final edited form as: Scand J Work Environ Health. 2010 Sep 13;36(6):499–508. doi: 10.5271/sjweh.3088

Table 3.

Adjusted mortality rate ratios (MRR)^a for lung cancer mortality in the subcohort of workers hired on or after start of follow-up predicted from Cox regression models using penalized splines in this study. [MWF=metalworking fluid; 95% CI=95% confidence interval; N/A=not available.]

Percentile	Early exposure to synthetic MWF (>20 years)^b			Recent exposure to synthetic MWF (≤20 years)^b			Synthetic MWF with biocide^{b, c}			Synthetic MWF without biocide^{b, c}
	mg/m³ per year	MRR	95% CI	mg/m³ per year	MRR	95% CI	mg/m³ per year	MRR	95% CI	mg/m³ per year	MRR	95% CI
25^th	0	N/A	..	0	N/A	..	0.24	0.99	0.90–1.09	0	N/A	..
50^th	0	N/A	..	0	N/A	..	0.98	0.96	0.91–1.02	0	N/A	..
75^th	0.03	1.00	0.99–1.02	0	N/A	..	2.26	0.92	0.91–0.93	0	N/A	..
90^th	1.46	1.02	1.01–1.03	0.62	0.93	0.90–0.95	5.33	0.82	0.73–0.92	0	N/A	..
99^th	14.18	1.27	0.97–1.66	8.62	0.34	0.14–0.81	37.48	0.24	0.06–0.99	11.60	1.08	0.92–1.28

Cox models were adjusted for straight MWF (mg/m³ per year), soluble MWF (mg/m³ per year), race, gender, plant, calendar year, and years since retirement.

Synthetic MWF in all models was treated as a linear term, but soluble MWF, straight MWF, calendar year, and years since retirement were treated as non-linear terms if degrees of freedom selected by Akaike information criterion (AIC) exceeded 1.0 and if P< 0.10.

Predicted MRR of synthetic MWF derived from models presented in Figure 3.