| MEASUREMENT PROPERTIES | |
| Limitations | <5 European languages (English) |
| Observations | |
| 1. RELIABILITY | |
| A. Internal Consistency | Tested |
| Cronbach's (Describe) |
For the BASFI questionnaire: ICC = 0.93 (0.90–0.95) |
| B. Reliability intraobserver or test-retest | Tested |
| Continuous scores: intraclass correlation coefficient (ICC) Dichotomus: Cohen kappa (Describe) |
All PBM were repeated twice with 30 s in between (test-retest reliability) and most tests consisted of both a “self-selected pace” and “maximal speed” trial. Good to excellent test-retest reliability was found in general, with variables ICC ranging from 0.765-0.997 for different tests (lower for sock tests, higher for stair climbing and cervical rotation). |
| C. Reliability interobserver or Measurement error | Tested |
| Standard error of measurement (SEM), smallest detectable change (SDC) or Limits of agreement (LoA) (Describe) |
SEM was clinically expressed in percent of total movement time. SEM% values ranged from 0.4% to 23.9%, excluding the pen (30.4%) and reach tests (32.0%). |
| 2. VALIDITY | |
| A. Content validity: face validity | Tested |
| Expert opinion (relevance and comprehensiveness) (Describe) |
For the questionnaire: Items were generated by an expert group of physiotherapists, researchers, rheumatologists, and patients (however the role of patients is not made explicit). |
| B. Construct Validity: Structural validity |
Tested |
| Hypotheses-testing | Tested |
| Cross-cultural validity | Not Tested |
| Brief Description |
The core set of the iBASFI items consisted of the STS speed test, the cervical rotation test, and height. This core set explained 59% of the variance in the BASFI, confirming convergent construct validity of the composite and successful reduction of items. No issues on colinearity were detected. |
| C. Criterion validity | Not Tested |
| Comparison with a 'gold standard' Continuous scores: correlations, ROC curves Dichotomus: Sensitivity & Specificity (Describe) |
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