| MEASUREMENT PROPERTIES | |
| Limitations | <5 European languages (English) |
| Observations | |
| 1. RELIABILITY | |
| A. Internal Consistency | Not Tested |
| Cronbach's (Describe) | |
| B. Reliability intraobserver or test-retest | Not Tested |
| Continuous scores: intraclass correlation coefficient (ICC) Dichotomus: Cohen kappa (Describe) |
The reliability of the instrument has not been assessed per se. The measures that constitute the scoring system have been routinely used in clinical trials and have been proven to be reliable. |
| C. Reliability interobserver or Measurement error | Tested |
| Standard error of measurement (SEM), smallest detectable change (SDC) or Limits of agreement (LoA) (Describe) |
The discriminatory MDA power of CPDAI was very good, with an AUC of 0.792 (95% CI 0.724 to 0.9850) |
| 2. VALIDITY | |
| A. Content validity: face validity | Tested |
| Expert opinion (relevance and comprehensiveness) (Describe) |
The CPDAI is based on a framework that was proposed by the Group for Research and Assessment of Psoriasis and Psoriatic Arthritis (GRAPPA) to guide treatment decisions in PsA. |
| B. Construct Validity: Structural validity |
Tested |
| Hypotheses-testing | Tested |
| Cross-cultural validity | Not Tested |
| Brief Description |
In order to extract components contributing to maximum variability in the data, a factor analysis was used to produce a solution using principal components extraction; the first rotated factor is most highly correlated with the swollen joint count and dactylitic digit count; the second rotated factor correlates with the PASI and DLQI, the third with the LEI and tender joint count, and the final factor is highly correlated with the HAQ |
| C. Criterion validity | Not Tested |
| Comparison with a 'gold standard' Continuous scores: correlations, ROC curves Dichotomus: Sensitivity & Specificity (Describe) |
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