Table 4.
Comparison of measurement characteristics and construct validity between IRT-based AAQ scores and different CAT versions with original AAQ scores
| Original AAQ score | IRT-based AAQ score | CAT-17 | CAT-10 | CAT-5 | |
|---|---|---|---|---|---|
| Mean test length | 17 items | 17 items | 8.0 items | 6.6 items | 4.8 items |
| AAQ score mean (SD) | 78.3 (17.3) | 78.5 (16.8) | 78.4 (16.7) | 78.4 (16.7) | 78.4 (16.6) |
| AAQ score range | 0.0–100.0 | 2.3–98.6 | 8.0–98.6 | 8.0–98.6 | 8.0–98.6 |
| RMSE | – | 1.71 | 5.02 | 5.05 | 5.39 |
| Bias (mean difference to original AAQ) | – | 0.17 | 0.11 | 0.13 | 0.16 |
| Pearson correlation with full AAQ (95% CI) | – | 1.00 [1.00, 1.00] | 0.96 [0.95, 0.96] | 0.96 [0.95, 0.96] | 0.95 [0.95, 0.96] |
| Pearson correlation H/KOOS ADL (95% CI) | 0.73 [0.71, 0.76] | 0.73 [0.70, 0.75] | 0.68 [0.65, 0.71] | 0.68 [0.65, 0.71] | 0.68 [0.65, 0.71] |
| Spearman correlation with SCT (95% CI) | − 0.68 [− 0.74, − 0.62] | − 0.68 [− 0.74, − 0.62] | − 0.66 [− 0.72, − 0.58] | − 0.66 [− 0.72, − 0.59] | − 0.66 [− 0.72, − 0.59] |
| Spearman correlation with TUG (95% CI) | − 0.61 [− 0.68, − 0.54] | − 0.62 [− 0.68, − 0.54] | − 0.60 [− 0.66, − 0.52] | − 0.60 [− 0.66, − 0.52] | − 0.60 [− 0.67, − 0.52] |
| Spearman correlation with CST (95% CI) | 0.60 [0.52, 0.67] | 0.60 [0.52, 0.67] | 0.60 [0.52, 0.67] | 0.60 [0.52, 0.67] | 0.60 [0.52, 0.67] |
AAQ animated activity questionnaire, CAT computer adaptive test, CI confidence interval, CST chair stands test, H/KOOS ADL ADL subscale of the knee disability and osteoarthritis outcome score (HOOS) or knee injury and osteoarthritis outcome score (KOOS), RMSE root mean square error, SCT stair climbing test, SD standard deviation, TUG timed up and go test