Table 2. Cox model HR and 95% CI for lung cancer mortality in lifetime smoky coal users in Xuanwei, China, 1976–1996a.

	Men and women		Men		Women
	HR (95% CI)	P-value	HR (95% CI)	P-value	HR (95% CI)	P-value
No stove change	1.00 (reference)		1.00 (reference)		1.00 (reference)
Stove change	0.52 (0.41–0.64)	<0.0001	0.62 (0.46–0.82)	0.001	0.41 (0.29–0.57)	<0.0001
Used annual average <2 tons of smoky coal	1.00 (reference)		1.00 (reference)		1.00 (reference)
Used annual average ⩾2 to <3 tons of fuel	1.61 (1.27–2.03)	<0.0001	1.27 (0.93–1.73)	0.133	2.07 (1.43–3.00)	0.0001
Used annual average ⩾3 to <4 tons of fuel	2.19 (1.73–2.79)	<0.0001	1.77 (1.29–2.43)	0.0004	2.70 (1.85–3.93)	<0.0001
Used annual average ⩾4 tons of fuel	2.37 (1.84–3.06)	<0.0001	1.69 (1.21–2.38)	0.002	3.32 (2.24–4.92)	<0.0001
No lung cancer in spouse	1.00 (reference)		1.00 (reference)		1.00 (reference)
Lung cancer in spouse	1.77 (1.43–2.18)	<0.0001	1.47 (1.07–2.02)	0.019	2.12 (1.60–2.82)	<0.0001
No lung cancer in parents, siblings, and children	1.00 (reference)		1.00 (reference)		1.00 (reference)
Lung cancer in parents, siblings, and children	1.36 (1.08–1.70)	0.008	1.48 (1.10–1.99)	0.010	1.20 (0.85–1.69)	0.311
No history of COPD	1.00 (reference)		1.00 (reference)		1.00 (reference)
History of COPD	1.24 (1.08–1.43)	0.003	1.33 (1.10–1.62)	0.004	1.19 (0.97–1.46)	0.103
No history of tuberculosis	1.00 (reference)		1.00 (reference)		1.00 (reference)
History of tuberculosis	1.38 (0.80–2.39)	0.252	1.95 (0.96–3.95)	0.065	0.89 (0.37–2.15)	0.789
<7 waking hours indoors per day, until 20 years old	1.00 (reference)		1.00 (reference)		1.00 (reference)
⩾7 waking hours indoors per day, until 20 years old	1.11 (0.98–1.26)	0.089	1.03 (0.86–1.23)	0.747	1.21 (1.02–1.45)	0.034
Average of <2 rooms in all houses throughout life	1.00 (reference)		1.00 (reference)		1.00 (reference)
Average of ⩾2 rooms in all houses throughout life	1.10 (0.97–1.25)	0.155	1.18 (0.98–1.42)	0.075	1.03 (0.85–1.24)	0.755
Illiterate	1.00 (reference)		1.00 (reference)		1.00 (reference)
Literate	1.19 (1.02–1.38)	0.023	1.15 (0.95–1.39)	0.146	1.27 (0.97–1.65)	0.082
Never coal miner	1.00 (reference)		1.00 (reference)		Not applicable
Ever coal miner	3.34 (2.56–4.36)	<0.0001	3.39 (2.57–4.47)	<0.0001	Not applicable
<20 years of smoking	1.00 (reference)		1.00 (reference)		Not applicable
⩾20 years of pipe smoking	0.86 (0.69–1.08)	0.197	0.84 (0.64–1.11)	0.223	Not applicable
20–40 years of cigarette smoking	1.21 (0.96–1.53)	0.114	1.22 (0.91–1.63)	0.179	Not applicable
⩾40 years of cigarette smoking	1.42 (1.04–1.94)	0.027	1.44 (0.99–2.09)	0.054	Not applicable
Never cooked	Not applicable		1.00 (reference)		Not applicable
Ever cooked	Not applicable		0.94 (0.73–1.22)	0.650	Not applicable
<20 years of cooking	1.00 (reference)		Not applicable		1.00 (reference)
20–40 years of cooking	1.27 (1.03–1.55)	0.023	Not applicable		1.45 (0.91–2.32)	0.121
⩾40 years of cooking	1.44 (1.12–1.86)	0.004	Not applicable		1.53 (0.92–2.54)	0.103

CIs=confidence intervals; HRs=hazard ratios.

^aCox models include the time-dependent variables for change to portable stove, average tons of fuel used annually (2–<3 tons, 3–<4 tons, ⩾4 tons, compared with <2 tons), years of smoking (20–40 years, ⩾40 years, compared with <20 years), and years of cooking (20–40 years, ⩾40 years, compared with <20 years), along with dummy variables for history of spousal lung cancer (yes vs no), family history of lung cancer (parents, siblings, or children) (yes vs no), history of chronic bronchitis (yes vs no), history of tuberculosis (yes vs no), number of hours spent indoors until the age of 20 years (<7 vs ⩾7 h), average number of rooms in all households throughout life (<2 rooms vs ⩾2 rooms), educational status (illiterate vs literate), and history of working as a miner (yes vs no). Sex-specific Cox-regression models include the same covariates, as well as, history of ever cooking (ever vs never) in men. Birth cohort effects are controlled by stratification within the model by 5-year intervals (born during 1917–1921, 1922–1926, 1927–1931, 1932–1936, 1937–1941, 1942–1946, and 1947–1951).