Table 5

Additive predictive value of proposed variables compared with the refit GAP index

ModelC-statistic (95% CI)Difference in C-statistic compared with GAP*NRI (%) (95% CI)*IDIevent (95% CI)*IDInon-event (95% CI)*IDI
(95% CI)P value
Original GAP index0.683 (0.624 to 0.742)−0.018 (−0.046 to 0.034)0.208−4.0 (−35.1 to 34.4)−0.003 (−0.005 to 0.012)−0.001 (−0.001 to 0.003)−0.004 (−0.005–0.015)
Refit GAP index0.701 (0.646 to 0.756)
GAP +6MWD††0.738 (0.686 to 0.789)0.037 (0.003 to 0.070)0.03146.6 (15.0 to 75.4)0.034 (0.005 to 0.083)0.007 (0.002 to 0.017)0.041 (0.006–0.101)
GAP +EH0.742 (0.691 to 0.793)0.041 (0.004 to 0.078)0.03188.5 (51.8 to 108.3)0.045 (0.013 to 0.084)0.009 (0.003 to 0.018)0.055 (0.016–0.100)
GAP +6 MWD††+EH0.756 (0.706 to 0.806)0.055 (0.011 to 0.098)0.01461.9 (26.9 to 102.9)0.062 (0.026 to 0.119)0.012 (0.005 to 0.025)0.074 (0.032–0.143)
DO-GAP index‡‡0.752 (0.701 to 0.802)0.050 (0.004 to 0.097)0.03546.1 (19.6 to 66.2)0.055 (0.022 to 0.101)0.011 (0.004 to 0.022)0.066 (0.026–0.122)
  • *Improvement comparisons made to the GAP index after refitting original GAP index to the derivation set.

  • †6MWD included as categorical variable.

  • ‡Model based on point-score index (see study design and methods for further detail).

  • DO-GAP, distance-oxygen-gender-age-physiology; EH, exertional hypoxia; GAP, gender-age-physiology; IDI, incremental discrimination improvement; 6MWD, 6 min walk test distance; NRI, net reclassification improvement.