Systematic review of the evidence relating FEV1decline to giving up smoking

Table 2 Distribution of study characteristics

Characteristic	Level	No. of studies	(%)	Characteristic	Level	No. of studies	(%)
Sex	Both	28	(59.6)	Year at end^a	1960-69	3	(6.4)
	Males only	19	(40.4)		1970-79	10	(21.3)
					1980-89	15	(31.9)
Lowest age	13-29	23	(48.9)		1990-99	14	(29.8)
	30-39	10	(21.3)		2000+	4	(8.5)
	40-49	8	(17.0)		Not known^b	1	(2.1)
	50-59	3	(6.4)
	60+	3	(6.4)	Follow-up (yr)	4-9	23	(48.9)
					10-14	13	(27.7)
Highest age^c	< 50	3	(6.4)		15-19	3	(6.4)
	50-59	12	(25.5)		20+	7	(14.9)
	60-69	8	(17.0)		Not known^b	1	(2.1)
	70+	24	(51.0)
				Study type	Cohort	43	(91.5)
Country	USA	13	(27.7)		Intervention	4	(8.5)
	Canada	2	(4.3)
	UK	6	(12.8)	Population	General	37	(78.7)
	France	2	(4.3)		Diseased^d	10	(21.3)
	Belgium	2	(4.3)
	Netherlands	3	(6.4)	Medical exclusions	Some	25	(53.2)
	Sweden	3	(6.4)		None	22	(46.8)
	Norway	2	(4.3)
	Denmark	1	(2.1)	Subjects (at start)	13-100	9	(19.1)
	Finland	1	(2.1)		101-500	10	(21.3)
	Poland	2	(4.3)		501-1,000	7	(14.9)
	Japan	4	(8.5)		1,001-5,000	15	(31.9)
	China	2	(4.3)		> 5,000	6	(12.8)
	Australia	1	(2.1)
	Multicountry	3	(6.4)	Betas adjusted	None	29	(61.7)
					Some	18	(38.3)
Year at start	1960-69	16	(34.0)
	1970-79	15	(31.9)
	1980-89	11	(23.4)
	1990-99	4	(8.5)
	Not known^b	1	(2.1)

^aYear at end of follow-up. ^bStudy 44 gave no information on timing, but since it was published in 2007 and involved follow-up of at most 3 years, it seems likely to have been conducted recently. ^cAt baseline. ^dAll four intervention studies comprised patients with specified medical conditions.

ISSN: 1741-7015