Systematic review with meta-analysis of the epidemiological evidence relating smoking to COPD, chronic bronchitis and emphysema

Table 9 Main meta-analyses for current or ever smoking of any product (or cigarettes, if not available)a

Preference	Statistic^b	COPD	CB	Emphysema
Ever smoking to current smoking	n	138	121	33
	F	2.47 (2.40-2.53)	2.42 (2.36-2.48)	3.32 (3.04-3.61)
	R	3.00 (2.71-3.32)	2.70 (2.51-2.90)	4.83 (3.46-6.73)
	H, P_H	10.61, < 0.001	5.61, < 0.001	9.95, < 0.001
Current smoking to ever smoking	n	139	121	33
	F	2.87 (2.79-2.95)	2.82 (2.75-2.90)	3.44 (3.13-3.78)
	R	3.46 (3.07-3.90)	3.27 (3.02-3.54)	5.05 (3.51-7.25)
	H, P_H	13.15, < 0.001	6.53, < 0.001	10.52, < 0.001

^a Within each study, results are selected in the following order of preference, within each sex, for: smoking status-ever, current or current, ever according to analysis; unexposed group-never any product, never cigarettes, other; smoking product-any, cigarettes (ignoring other products), cigarettes only; overlapping studies-principal, subsidiary; and then for single sex results in preference to combined sex results. Results adjusted for the most potential confounders are selected.
^b n = number of estimates combined, F = fixed-effect meta-analysis RR (95% CI), R = random-effects meta-analysis RR (95% CI), H = heterogeneity chisquared per degree of freedom.

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