Forced expiratory volume in one second: why dichotomise?

Numerous epidemiological surveys have tried to evaluate the effects of exposures relevant to pulmonary disease.' A number of studies have analysed forced expiratory volume in one second (FEVI) using linear regression analysis, thus enabling adjustment for age, height, and sex as well as potential confounding variables. Within the last few years, studies analysing dichotomous FEV, variables with different cutoff points in multivariate regression models have been published.23 As there seems to be no obvious reason for dichotomising the continuous FEVI, we have compared the results of the two different approaches to analysis of FEV,.