The diagnostic value of the forced expiratory time

Abstract

To the Editor. —Schapira et al 1 concluded that the forced expiratory time (FET) demonstrates moderately good performance as a diagnostic test for obstructive airways disease (OAD). In attempting to explain how we found the opposite to be true in a study of 205 plumbers and pipefitters, 2 the authors pinpointed their study group's advanced age and higher prevalence of disease. To assess the explanatory power of these two factors, we reanalyzed our data using the authors' criterion standard for OAD (forced expiratory volume at 1 second [FEV 1 %], less than 70%). Performing separate analyses for those subjects younger than 60 years and those older than 60 years we recalculated the sensitivity and specificity of FET at various cutoff values. Last, we relied on the authors' observed disease prevalence of 50% to determine FET's overall accuracy: (T + +T - )/(T + +F - +T - +F + ) (Table). The tabulated data reveal that FET performed