Table 3

Validation of subjects statements as compared with expired carbon monoxide, in a sub-sample of the population

Strategy A Strategy B
Comparison between self reported smoking status and expired CO ⩾7 ppm
At inclusion, in the whole population
  κ coefficient (95% CI)0.61 (0.54, 0.67)0.56 (0.46, 0.65)
 At one year follow up, among subjects who were smokers at inclusion
  κ coefficient (95% CI)0.38 (0.20, 0.56)0.37 (0.12, 0.62)
Among smokers, correlation between expired carbon monoxide and number of cigarettes/day3-150
  r 0.570.51
 One year follow up
  r 0.540.57
  • 3-150 Given the skewness of the distribution, cigarette consumption was log transformed. The consumption of occasional smokers (<1 cig/day) was arbitrarily fixed at 0.2 cigarettes/day as many occasional smokers reported smoking 1 cig/week.