Table 3.

Pooled relative risks (95% confidence intervals) of amyotrophic lateral sclerosis by smoking category at baseline

	No. of cases	Person- years	RRa (95% CI)	p	p for heterogeneityc	RRb (95% CI)	P	p for heterogeneityc
All
Never smokers	258	5,280,234	1.0 (ref)			1.0 (ref)
Former smokers	450	5,401,310	1.44 (1.23–1.68)	<0.0001	0.97	1.46 (1.25–1.71)	<0.0001	0.95
Current smokers	108	1,905,109	1.42 (1.07–1.88)	0.016	0.26	1.34 (0.99–1.82)	0.06	0.2
Ever smokers	558	7,314,081	1.42 (1.22–1.66)	<0.0001	0.97	1.43 (1.23–1.66)	<0.0001	0.83
1–20 pack-years	221	3,652,575	1.31 (1.07–1.57)	0.004	0.74	1.31 (1.09–1.57)	0.004	0.77
21–35 pack-years	169	1,793,611	1.71 (1.30–2.25)	<0.0001	0.21	1.70 (1.26–2.28)	<0.0001	0.16
>35 pack-years	152	1,671,689	1.43 (1.13–1.79)	0.002	0.37	1.42 (1.10–1.84)	0.008	0.27
Pack-years:
P for trend			0.001		0.30	0.004		0.24
P for trend (smokers only)			0.60		0.07	0.60		0.07
Male
Never smokers	134	1,815,677	1.0 (ref)			1.0 (ref)
Former smokers	300	2,978,458	1.26 (1.03–1.55)	0.03	0.98	1.30 (1.06–1.89)	0.01	0.99
Current smokers	52	595,189	1.35 (0.97–1.87)	0.07	0.91	1.36 (0.98–1.89)	0.07	0.87
Ever smokers	352	3,577,576	1.28 (1.04–1.56)	0.02	0.97	1.31 (1.07–1.61)	0.009	0.96
1–20 pack-years	110	1,557,353	1.02 (0.79–1.31)	0.90	0.98	1.03 (0.80–1.34)	0.80	0.99
21–35 pack-years	127	928,757	1.80 (1.40–2.31)	<0.0001	0.38	1.84 (1.44–2.36)	<0.0001	0.40
>35 pack-years	107	1,006,466	1.25 (0.90–1.76)	0.20	0.25	1.31 (0.91–1.88)	0.15	0.21
Pack-years:
P for trend			0.04		0.14	0.03		0.12
P for trend (smokers only)			0.38		0.05	0.24		0.09
Female
Never smokers	124	3,464,557	1.0 (ref)			1.0 (ref)
Former smokers	150	2,422,852	1.65 (1.27–2.14)	<0.001	0.34	1.65 (1.29–2.12)	<0.001	0.35
Current smokers	56	1,309,920	1.47 (0.86–2.49)	0.16	0.05	1.34 (0.79–2.28)	0.28	0.05
Ever smokers	206	3,736,504	1.56 (1.16–2.08)	0.003	0.19	1.52 (1.15–2.02)	0.004	0.22
1–20 pack-years	111	2,095,223	1.64 (1.19–2.27)	0.003	0.22	1.62 (1.18–2.21)	0.003	0.25
21–35 pack-years	42	864,854	1.41 (0.96–2.07)	0.08	0.38	1.36 (0.93–1.98)	0.11	0.40
>35 pack-years	45	665,224	1.73 (1.11–2.68)	0.02	0.24	1.64 (1.04–2.58)	0.03	0.22
Pack-years:
P for trend			0.08		0.21	0.12		0.19
P for trend, (smokers only)			0.73		0.18	0.07		0.16

^aadjusted for age, sex (for analysis of total)

^badjusted for age, body mass index, physical activity, education level, sex (for analysis of total)

^cp values for the tests of heterogeneity between studies were calculated using the Q statistic

RR=relative risk; CI= confidence interval