To further assess the estimated FVC3, we evaluated the correlations with actual FVC and detection of obstruction in the subset of validation set spirograms that achieved (34%) vs those that did not achieve an expiratory plateau (66%). The strength of the correlations, the variances, and the statistical significance of the predictive equations were similar in both subsets (ie, in those achieving an expiratory plateau, R2 = 0.94, RMSE = 0.217, p < 0.0001; and in those not achieving an expiratory plateau, R2 = 0.94, RMSE = 0.238, p < 0.0001). The sensitivity, specificity, PPV, and NPV were similar in the group of spirograms with expiratory plateau and in the group without a valid expiratory plateau, ie, 92%, 84%, 60%, 97%, and 94%, 91%, 88%, 95%, respectively. Also, dichotomizing the spirograms in the validation set by those in which estimated FVC3 underestimated measured FVC vs those in which the estimated FVC3 overestimated the measured FVC group, we observed that the predictive equation produced the following sensitivities, specificities, PPVs, and NPVs: 100%, 92%, 88%, 100% and 68%, 100%, 100%, 81%, respectively. The κ statistic degree of agreement in detecting obstruction varied between 0.79 and 0.89 among different subgroups (plateau vs nonplateau, underestimated vs overestimated FVC).