Dose-response relationship of lung cancer to amount smoked, duration and age starting

Table 16 Age of starting to smoke by current smokers - inverse-variance weighted simple regression analyses of β₁ based on best-fitting power model

Factor	Level	n	β1 (95%CI)	P1	RR for 15 yr start
All		27	0.18 (0.16-0.20)		7.80
Sex	Male	17	0.19 (0.17-0.21)	< 0.05	9.49
	Female	9	0.14 (0.11-0.17)		5.14
	Combined	1	0.14 (0.04-0.25)		5.40
Study type	Case-control	10	0.15 (0.11-0.20)	NS	5.94
	Prospective	17	0.18 (0.16-0.20)		8.37
Continent	North America	9	0.21 (0.19-0.23)	< 0.01	11.49
	Europe	9	0.16 (0.13-0.19)		6.38
	Asia	8	0.14 (0.11-0.17)		5.17
	Other	1	0.19 (0.08-0.31)		9.50
Publication year2	< 1990	11	0.15 (0.11-0.19)	< 0.01	5.59
	1990-1994	4	0.14 (0.11-0.17)		5.17
	1995-1999	12	0.20 (0.18-0.22)		10.37
Product3	Any product	3	0.17 (0.11-0.24)	< 0.05	7.65
	Cigarettes +/-	16	0.19 (0.17-0.21)		9.09
	Cigarettes only	8	0.13 (0.09-0.17)		4.69
Unexposed	Never cigarettes	4	0.19 (0.13-0.25)	NS	9.05
	Never any product	23	0.17 (0.15-0.20)		7.66
Grouped midpoint age (yr)	< 50	7	0.18 (0.13-0.23)	NS	7.73
	50-59	9	0.21 (0.17-0.25)		10.98
	60+	11	0.17 (0.14-0.19)		6.88
Cases in smokers	< 100	12	0.14 (0.11-0.17)	< 0.001	5.09
	100 to < 200	7	0.20 (0.16-0.24)		9.88
	200 to < 500	4	0.17 (0.23-0.20)		7.02
	500 to < 1000	3	0.23 (0.20-0.26)		14.57
	1000+	1	0.15 (0.11-0.19)		5.71

¹Probability values for factor considered, presented as < 0.001, < 0.01, < 0.05, < 0.1 or not significant (NS) (P≥ 0.1);

²Of principal publication for the study;

³Any product = Smokes cigarettes and/or pipes and/or cigars; Cigarettes +/- = Smokes cigarettes with or without other products (pipes, cigars).