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

Forey, Barbara A; Thornton, Alison J; Lee, Peter N

doi:10.1186/1471-2466-11-36

Table 4 Distribution of the main characteristics of the relative risks (principal studies only^a)

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

RRs	Characteristic	Level	Outcome
			COPD	CB	Emphysema	Total
All RRs	Total	Total	1,342	1,311	210	2,863
	Study type	Case/control	194	162	0	356
		Prospective	414	86	66	566
		Cross-sectional	734	1,063	144	1,941
	Sex	Both	289	215	35	539
		Male	660	552	114	1,326
		Female	393	544	61	998
	Adjusted for any variable	No	605	677	93	1,375
		Yes	737	634	117	1,488
	Adjusted for age	No	624	758	99	1,481
		Yes	718	553	111	1,382
	Adjusted for other confounders^b	No	1,051	1,135	187	2,373
		Yes	291	176	23	490
	Derivation	Original or 2 × 2^c	409	478	86	973
		Other derived	933	833	124	1890
RRs for major smoking indices	Total	Total	551	547	105	1,203
	Exposed group: smoking status	Ever	185	186	45	416
		Current	214	205	36	455
		Ex	152	156	24	332
	Exposed group: smoking product	Any product	166	211	29	406
		Cigarettes (+/- other)	314	269	62	645
		Cigarettes only	71	67	14	152
	Unexposed	Never any product	283	335	53	671
		Never cigarettes	261	206	52	519
		Other^d	7	6	0	13
RRs for all dose-response indices	Total	Total	791	764	105	1,660
	Exposed group: smoking status	Ever	221	138	19	378
		Current	415	492	83	990
		Ex	155	134	3	292
	Exposed group: smoking product	Any product	64	176	8	248
		Cigarettes (+/- other)	525	399	69	993
		Cigarettes only	202	189	28	419
	Unexposed	Never (any or cigs)	389	387	60	836
		Low^e (any or cigs)	318	295	38	651
		Current (any or cigs)	33	32	0	65
		Other^f/not applicable^g	51	50	7	108
RRs for amount smoked	Total	Total	335	474	65	874
	Exposed group: smoking status	Ever	3	51	9	63
		Current	323	413	55	791
		Ex	9	10	1	20
Sets for amount smoked		vs. never (any or cigs)	66	94	14	174
		vs. low amount	65	97	16	178
		vs. non^h	2	9	0	11
		Non categorical	9	11	3	23
RRs for age started	Total	Total	78	50	6	134
	Exposed group: smoking status	Ever	6	38	0	44
		Current	65	12	6	83
		Ex	7	0	0	7
Sets for age started		vs. never (any or cigs)	12	4	2	18
		vs. later start	21	9	2	32
		vs. non^h	1	0	0	1
		Non categorical	6	0	0	6
RRs for pack-years	Total	Total	225	88	15	328
	Exposed group: smoking status	Ever	208	48	5	261
		Current	14	30	10	54
		Ex	3	10	0	13
Sets for pack-years		vs. never (any or cigs)	34	15	3	52
		vs. low pack-years	41	15	3	59
		Non categorical	25	9	2	36
RRs for duration of smoking	Total	Total	17	39	17	73
	Exposed group: smoking status	Ever	4	1	5	10
		Current	13	37	12	62
		Ex	0	1	0	1
Sets for duration of smoking		vs. never (any or cigs)	2	6	3	11
		vs. low duration	2	6	2	10
		Non categorical	5	5	0	10
RRs for duration of quitting	Total	Total	136	113	2	251
Sets for duration of quitting		vs. never (any or cigs)	13	13	0	26
		vs. current	12	11	0	23
		vs. long term ex	14	11	0	25
		vs. recent ex	14	11	0	25
		Non categorical	2	3	2	7

^a The number of additional RRs recorded for subsidiary studies was 236 for COPD, 378 for CB and 61 for emphysema.
^b Variables other than sex, age and aspects of smoking
^c Calculated directly from 2 × 2 or 2 × 2 × ℓ table
^d Never or low amount (any or cigs)
^e Low in terms of the measure of exposure (e.g. low amount for amount smoked, later starting for age started)
^f Never or low amount (any or cigs); or never and ex smokers combined
^g Dose-response RR not for categorical data
^h Never and ex smokers combined

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ISSN: 1471-2466

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