Table 4.

Changing to the use of a portable stove or stove with chimney among lifetime smoky and smokeless coal users and risk of ischaemic heart disease and stroke mortality among women in the Xuanwei cohort, 1976–2011

	No stove intervention/change		Any stove change/intervention HR(95% CI)a,b		P-value	P-heterogeneity (coal type)c
	# cases	HR (95% CI)	# cases	HR (95% CI)
Lifetime smoky or smokeless coal users
Ischaemic heart disease	14	1.0 (ref)	76	0.4 (0.2–0.7)	0.002	0.15
Stroke	34	1.0 (ref)	286	1.2 (0.8–1.7)	0.48	0.15
Lifetime and exclusive smoky coal users
Ischaemic heart disease	7	1.0 (ref)	41	0.6 (0.2–1.4)	0.23
Stroke	30	1.0 (ref)	192	1.2 (0.8–1.8)	0.43
Lifetime and exclusive smokeless coal users
Ischaemic heart disease	7	1.0 (ref)	24	0.2 (0.1–0.5)	0.001
Stroke	4	1.0 (ref)	72	1.3 (0.4–4.1)	0.62

^aAnalyses for any stove improvement include subjects who changed to using either a portable stove or stove with chimney (including subjects who used both of these stove types at some point in their life). Models exclude subjects who did not permanently use these stoves after the intervention.

^bAdjusted for education (categorical variable no formal school vs any formal school), birth cohort [categorical six-level variable: 1917–21 (ref.), 1922–26, 1927–31, 1932–36, 1937–41, 1942–46, 1947–51), average tonnage of smoky or smokeless coal use for given year (time-dependent variable), cumulative years of cooking (<20, 20–40, >40 years), average number of hours spent indoors doing activities other than sleeping (continuous time-dependent variable), average number of rooms in home during lifetime, average number of people in home during lifetime, follow-up period (retrospective or prospective follow-up) and age.

^c P-heterogeneity calculated including cross-product terms (stove improvement x coal type) in models that only included lifetime and exclusive users of smoky and smokeless coal users.