| MEASUREMENT PROPERTIES | |
| Limitations | English only |
| Observations | |
| 1. RELIABILITY | |
| A. Internal Consistency | Tested |
| Cronbach's (Describe) |
Good internal consistency. Cronbach’s alpha range 0.77-0.96 |
| B. Reliability intraobserver or test-retest | Tested |
| Continuous scores: intraclass correlation coefficient (ICC) Dichotomus: Cohen kappa (Describe) |
Good test-retest reliability. ICCs ranged 0.89–0.96. In participants reporting ‘no change’ during the test-retest (3–5 days later), ICC values were high for each domain: 0.89 on organ-specific symptoms, 0,91 on systemic symptoms, 0,95 on treatment side effects, 0,96 on social and emotional impact, 0,95 on concerns about the future, and 0,96 on physical function. |
| C. Reliability interobserver or Measurement error | Tested |
| Standard error of measurement (SEM), smallest detectable change (SDC) or Limits of agreement (LoA) (Describe) |
Distribution-based estimates of minimal change (SEM and MDC90), which relate to the reliability (ICC) of each scale, were all appropriate and will be useful for calculating sample size in future studies. SEM ranged 4,95-8,25. MDC90 ranged 11.55-22.75. |
| 2. VALIDITY | |
| A. Content validity: face validity | Tested |
| Expert opinion (relevance and comprehensiveness) (Describe) |
In-depth qualitative interviews with 50 patients from UK, USA and Canada were used to produce themes of interest in AAV. Underpinning themes were then recast as candidate questionnaire questions, and these items were reduced and refined via piloting and cognitive interviewing. The final 29-item AAv-PRO questionnaire comprises the following six domains: ‘organ symptoms severity (OSS)’, ‘systemic symptoms severity (SSS)’, ‘treatment side effects (TSE)’, ‘social and emotional impact (SEI)’, ‘concerns about the future (CAF)’ and ‘physical function (PF)’. The domains comprehensively address symptom severity, and different aspects of HRQoL, by providing a profile of the overall impact of AAV and its treatment on patients’ everyday life. The international steering committee includes four patient partners, and patients have played a key role within every stage of the AAV-PRO development. |
| B. Construct Validity: Structural validity |
Tested |
| Hypotheses-testing | Tested |
| Cross-cultural validity | Not Tested |
| Brief Description |
A longitudinal survey of patients with AAV recruited via Vasculitis UK and the Vasculitis Patient-Powered Research Network (USA and Canada) was conducted to define the final scale structure and validate the AAV-PRO. The formal process of the reduction and determination of scale structure was guided by Exploratory Factor Analysis (EFA), Rasch analysis and from insights from the conceptual framework. The identified domains each fit the Rasch unidimensional model (Item Trait Interaction p>0,01). |
| C. Criterion validity | Tested |
| Comparison with a 'gold standard' Continuous scores: correlations, ROC curves Dichotomus: Sensitivity & Specificity (Describe) |
Convergent validity: As hypothesized, moderate to high Pearson correlations between baseline AAV-PRO domains and generic EQ-5D-5L index scores were obtained: range r -0,55 to -0,78, all p<0,0001 |