| MEASUREMENT PROPERTIES | |
| Limitations | >=5 European languages (English) |
| Observations | |
| 1. RELIABILITY | |
| A. Internal Consistency | Tested |
| Cronbach's (Describe) |
The scores using 9 and 12 domains had very similar internal consistency (Cronbach’s α 0.93–0.94) |
| B. Reliability intraobserver or test-retest | Tested |
| Continuous scores: intraclass correlation coefficient (ICC) Dichotomus: Cohen kappa (Describe) |
ICC for the PsAID-12: 0.95 (95% CI 0.92 to 0.96); 0.91 (95%CI 0.87 to 0.94). ICC for the PsAID-9: 0.94 (95%CI 0.91 to 0.96) |
| C. Reliability interobserver or Measurement error | Tested |
| Standard error of measurement (SEM), smallest detectable change (SDC) or Limits of agreement (LoA) (Describe) |
The PsAID questionnaire was completed at baseline, 1 week and 3 months (follow-up, group 2 only), and absolute reliability was determined by the SE of measurement (SEM): 0.51. |
| 2. VALIDITY | |
| A. Content validity: face validity | Tested |
| Expert opinion (relevance and comprehensiveness) (Describe) |
Twelve patient research partners identified 16 important domains of health, based on their personal experience. In a priority exercise, 139 PsA patients ranked these domains in order of importance and the 12 highest ranked domains were retained. A comitee of experts (14 physicians, including one dermatologist, two health professionals and the 12 patient research partners) elaborated one question to assess each of these 12 domains of health. |
| B. Construct Validity: Structural validity |
Tested |
| Hypotheses-testing | Tested |
| Cross-cultural validity | Tested |
| Brief Description |
Factor analysis revealed a 2-factor result defined as the PsAID Symptom Score and the PsAID Skin Score. Multivariable analysis showed that the PsAID-12 is determined by the articular disease activity (cDAPSA, p < 0.0001), severity of psoriasis (PsO; physician’s global assessment, p < 0.0001), and the presence of a coexisting fibromyalgia (FM; p < 0.0001). |
| C. Criterion validity | Tested |
| Comparison with a 'gold standard' Continuous scores: correlations, ROC curves Dichotomus: Sensitivity & Specificity (Describe) |
Comparison of 12 and 9 domains in terms of psychometric properties showed no improvement with the three additional domains, and the correlation and agreement between results with 9 and 12 domains was high. |