Agreement between central readers for various definitions of a positive MRI-SIJ for structural lesions on patient level
| Definition 1: ≥1 erosion or ≥1 fatty lesion or ankyloses | Definition 2: ≥1 erosion | Definition 3: ≥2 erosions | Definition 4: ≥3 erosions | Definition 5: ≥1 fatty lesion | |
|---|---|---|---|---|---|
| PPA (%) | 61.8 | 36.7 | 32.7 | 25.7 | 55.7 |
| NPA (%) | 66.0 | 78.4 | 84.3 | 88.4 | 84.3 |
| κ (95% CI) | 0.29 (0.22 to 0.36) | 0.22 (0.16 to 0.29) | 0.23 (0.15 to 0.30) | 0.19 (0.11 to 0.27) | 0.40 (0.32 to 0.48) |
| Definition 6: ≥2 fatty lesions | Definition 7: ≥3 fatty lesions | Definition 8: ankylosis | Definition 9: ≥3 erosions and/or fatty lesions | ||
| PPA (%) | 55.3 | 58.8 | 26.5 | 56.8 | |
| NPA (%) | 88.9 | 92.2 | 79.1 | 85.7 | |
| κ (95% CI) | 0.45 (0.36 to 0.53) | 0.51 (0.42 to 0.60) | 0.06 (−0.01 to 0.14) | 0.44 (0.36 to 0.51) |
κ in bold represent κ >0.40.
MRI-SIJ, MRI of the sacroiliac joints; NPA,negative percent agreement; PPA, positive percent agreement.