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Table 13 Meta-analyses for pack-yearsa

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

Pack-years

Statisticb

COPD

CB

Emphysema

Number of setsc

 

28

11

3

About 5d, g

N

23

10

Insufficient data

 

F

1.13 (1.06-1.20)

2.11 (1.74-2.55)

 
 

R

1.25 (1.09-1.44)

1.74 (1.17-2.58)

 
 

H, PH

2.06, < 0.01

2.85, < 0.01

 

About 20e, g

N

11

8

Insufficient data

 

F

1.68 (1.58-1.79)

4.54 (3.69-5.58)

 
 

R

2.53 (1.87-3.43)

4.54 (3.69-5.58)

 
 

H, PH

4.44, < 0.001

0.63, NS

 

About 45e, g

N

15

8

Insufficient data

 

F

3.14 (2.97-3.32)

7.33 (5.98-8.97)

 
 

R

3.69 (2.79-4.86)

7.04 (5.06-9.79)

 
 

H, PH

6.34, < 0.001

1.82, < 0.1

 

Highest v lowest

N

31

11

3

 

F

2.82 (2.69-2.97)

2.52 (2.25-2.82)

1.86 (1.40-2.47)

 

R

2.80 (2.37-3.30)

3.09 (2.33-4.10)

2.42 (1.25-4.70)

 

H, PH

4.09, < 0.001

2.23, < 0.05

1.79, NS

  1. 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.
  2. 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).
  3. c Number of sets of RRs available for the key value analysis, where base for comparison is never smoked.
  4. d Category for which results are provided includes 5 pack-years but does not include 20 pack-years.
  5. e Category for which results are provided includes 20 pack-years but does not include 5 or 45 pack-years.
  6. f Category for which results are provided includes 45 pack-years but does not include 20 pack-years.
  7. g Base for comparison is never smoked.