As is evident from the ORs in Fig 1, chronic bronchitis was more strongly influenced by TTFC than was emphysema. There are a few possible explanations for our finding of a stronger association for chronic bronchitis, compared to emphysema. First, TTFC may be more strongly associated with chronic bronchitis. Secondly, reporting for chronic bronchitis may be more accurate. Finally, chance must be considered since the confidence intervals do overlap.
