Table 3

Sensitivity analysis

Pretest Prob. (%)SpA featuresPost-test prob. (%)
The disease prevalence (pretest probability) and enthesitis were chosen as examples to illustrate effects of variation of these parameters on the post-test probability. A range of 1–10% for the disease prevalence and the consecutive post-test probabilities are given using constant test features (presence of IBP, HLA-B27, and uveitis). Likewise, we chose different LRs (resulting from different sensitivities and specificities) of the test parameter “enthesitis” using either a disease prevalence of 5% (assumed to be representative throughout the study) or also other possible prevalences of 3% and 7%, respectively.
*Figures in bold indicate figures that are varied in this sensitivity analysis (either for disease prevalence or for sensitivity and specificity of enthesitis). The resulting post-test probabilities are also shown in bold; †figures assumed to be representative for either prevalence or SpA features which were taken for the calculations throughout the study; ‡the LR of 2.5 results from a sensitivity of 25% and a specificity of 90% (see table 1; Boyer et al27); §the LR of 7.8 results from a sensitivity of 47% and a specificity of 94% (see table 1; Collantes-Estevez et al28).
1*IBP (LR 3.1)†HLA-B27 (LR 9.0)‡†Uveitis (LR 7.3)† 67
2 IBP (LR 3.1)HLA-B27 (LR 9.0)Uveitis (LR 7.3) 80
3 IBP (LR 3.1)HLA-B27 (LR 9.0)Uveitis (LR 7.3) 86
4 IBP (LR 3.1)HLA-B27 (LR 9.0)Uveitis (LR 7.3) 89
5†IBP (LR 3.1)HLA-B27 (LR 9.0)Uveitis (LR 7.3)91
7 IBP (LR 3.1)HLA-B27 (LR 9.0)Uveitis (LR 7.3) 94
10 IBP (LR 3.1)HLA-B27 (LR 9.0)Uveitis (LR 7.3) 96
5†IBP (LR 3.1)HLA-B27 (LR 9.0)Enthesitis (LR 3.4)†83
5IBP (LR 3.1)HLA-B27 (LR 9.0)Enthesitis (LR 2.5) 78
5IBP (LR 3.1)HLA-B27 (LR 9.0)Enthesitis (LR 7.8)§ 91
3 IBP (LR 3.1)HLA-B27 (LR 9.0)Enthesitis (LR 2.5) 68
7 IBP (LR 3.1)HLA-B27 (LR 9.0)Enthesitis (LR 7.8)§ 94