Table 5.

Multiplicative interaction between metal and smoking exposure for prevalence of COPD within the Jinchang Cohort Study membership.

Pack-Years	Occupational Category, OR (95% CI)
	Low (Office Workers)		Medium (Production Workers)		High (Smelting/Refining Workers)
	OR (95% CI)	p	OR (95% CI)	p	OR (95% CI)	p
Nonsmokers	1.0 (Reference)		1.41 (0.83–2.41)	0.17	1.62 (0.94–2.80)	0.12
~20	1.12 (0.44–2.87)	0.90	0.58 (0.23–1.44)	0.70	0.90 (0.39–2.06)	0.24
21–39	1.55 (0.68–3.50)	0.13	2.21 (1.23–3.97)	0.00	2.89 (1.50–5.56)	0.00
40~	2.08 (0.97–3.86)	0.00	2.59 (1.43–4.70)	0.00	4.60 (2.29–9.21)	0.00
p for trend	p < 0.01		p < 0.01		p < 0.01
p-interaction	p < 0.01