Reclassification tables for the Diamond & Forrester model and the Pryor model are presented in Tables 4 and 5. The addition of CTCS to Diamond & Forrester resulted in reclassification of 47.2% of patients of whom 73.3% were correctly reclassified. The reclassification calibration statistic (RCS) indicated a strong lack of fit for the Diamond & Forrester model (p < 0.00001) which decreased substantially when CTCS was added to the model (p < 0.01). The NRI (net reclassification improvement) was 33.6% (p < 0.0001) and the IDI (integrated discrimination improvement) was also statistically significant (18.8%, p < 0.001) indicating improvement in the classification of cases and non-cases in probability categories and improvement in discrimination between cases and non-cases.
Table 4 Probability of coronary artery disease: reclassification table after addition of CTCS to the Diamond and Forrester (model 1)
Probability category based on model 1 Probability category based on model 1 + CTCS Total, n (%)
<30% ≥30–50% ≥50–70% ≥70%
<30%
 N (%) 51 (67.1) 19 (25.0%) 4 (5.2) 2 (2.6) 76 (29.9)
 Observed probability, % 11.8 36.8 50.0 100.0 22.4
≥30–50%
 N (%) 25 (39.7) 13 (20.6) 19 (30.2) 6 (9.5) 63 (28.4)
 Observed probability, % 0.0 23.1 68.4 50.0 30.2
≥50–70%
 N (%) 4 (11.1) 5 (13.9) 6 (16.7) 21 (58.3) 36 (14.2)
 Observed probability, % 25 80.0 50.0 66.7 61.1
≥70%
 N (%) 5 (6.3) 2 (2.5) 8 (10.1) 64 (81.0) 79 (31.1)
 Observed probability, % 0.0 50.0 37.5 95.3 82.3
 
Total
 N (%) 85 (33.5) 39 (15.4) 37 (14.6) 93 (36.6) 254 (100.0)
 Observed probability, % 8.2 38.5 56.8 86.0 48.4
CTCS computed tomography coronary calcium score
Table 5 Probability of coronary artery disease: reclassification table after addition of CTCS to the model published by Pryor et al. (model 2)
Probability category based on model 2 Probability category based on model 2 + CTCS Total, n (%)
<30% ≥30–50% ≥50–70% ≥70%
<30%
 N (%) 76 (85.4) 10 (11.2) 2 (2.3) 1 (1.1) 89 (35.0)
 Observed probability, % 9.2 40.0 100.0 100.0 15.7
≥30–50%
 N (%) 10 (27.0) 10 (27.0) 12 (32.4) 5 (13.5) 37 (14.6)
 Observed probability, % 10.0 20.0 50.0 100.0 37.8
≥50–70%
 N (%) 7 (13.5) 6 (11.5) 15 (28.9) 24 (46.2) 52 (20.5)
 Observed probability, % 0.0 50.0 73.3 66.7 57.7
≥70%
 N (%) 3 (4.0) 3 (4.0) 9 (11.8) 61 (80.3) 76 (29.9)
 Observed probability, % 33.3 0.0 66.7 95.0 85.5
 
Total
 N (%) 96 (37.8) 29 (11.4) 38 (15.0) 91 (35.8) 254 (100.0)
 Observed probability, % 9.4 31.0 65.8 87.9 48.4
CTCS computed tomography coronary calcium score