How much is lung function affected by smoking and occupation? Dichotomy of continuous variables can change the results
Vestbo, J.; Knudsen, K.M.; Rasmussen, F.V.
Ugeskrift for Laeger 155(30): 2338-2340
1993
ISSN/ISBN: 0041-5782 PMID: 8346576 Document Number: 418845
Data from a cross-sectional study of 1045 men comprising a random population sample (768 men) and a sample of cement workers (277 men) were analyzed in order to examine the effects of smoking and occupation on forced expiratory volume in one second (FEV1). The continuous FEV1 variable and five dichotomous FEV1 variables based on % of predicted were analyzed. Differences between the "relative importance" of smoking and occupation were found to depend on the choice of the FEV1 variable. The effects of occupation compared with the effects of smoking varied considerably with different FEV1 variables, continuous or dichotomized at different cut-off levels. We conclude that comparison of surveys utilizing different FEV1 variables must be made with caution.