Duration of quitting | Statisticb
| COPD | CB |
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Number of setsc
| Â | 10 | 11 |
About 12 yearsd, g
| n | 10 | 9 |
 | F | 3.45 (2.96-4.01) | 1.40 (1.21-2.62) |
 | R | 2.12 (1.06-4.26) | 2.20 (1.33-3.65) |
 | H, PH
| 12.74, < 0.001 | 8.04, < 0.001 |
About 7 yearse, g
| n | 3 | 5 |
 | F | 8.15 (5.88-11.28) | 1.83 (1.49-2.25) |
 | R | 4.94 (1.21-20.07) | 2.36 (1.29-4.32) |
 | H, PH
| 14.80, < 0.001 | 6.52, < 0.001 |
About 3 yearsf, g
| n | 3 | 7 |
 | F | 3.58 (2.44-5.25) | 2.16 (1.82-2.57) |
 | R | 4.08 (0.80-20.77) | 2.42 (1.73-3.38) |
 | H, PH
| 16.66, < 0.001 | 2.79, < 0.05 |
Shortest v longest | n | 10 | 11 |
 | F | 2.20 (1.76-2.76) | 1.29 (1.06-1.56) |
 | R | 2.21 (1.24-3.94) | 1.25 (0.99-1.59) |
 | H, PH
| 4.88, < 0.001 | 1.29, NS |
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a Within each study, results are selected in the following order of preference, within each sex, for: smoking status-current, ever; unexposed group (where relevant)-never any product, never cigarettes; smoking product-cigarettes (ignoring other products), cigarettes only, any product; 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.
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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, PH = probability value for heterogeneity expressed as p < 0.001, p < 0.05, p < 0.1 or NS (p ≥ 0.1).
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c Number of sets of RRs available for the key value analysis, where base for comparison is never smoked. No data available for emphysema.
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d Category for which results are provided includes quit 12 years ago but does not include quit 7 years ago.
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e Category for which results are provided includes quit 7 years ago but does not include quit 3 or 12 years ago.
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f Category for which results are provided includes quit 3 years ago but does not include quit 7 years ago.
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g Base for comparison is never smoked.