| MEASUREMENT PROPERTIES | |
| Limitations | <5 European languages (English) |
| Observations |
For the FiRST development, a study advisory committee, composed of four rheumatologists and two neurologists experienced in FMS management and clinical research, together with a psychometrician, compiled an initial list of items representative of FMS dimensions (53 items). Structured interviews were then carried out with 10 FM patients, which made it possible to decrease the number of items to 10 in the second version of the questionnaire. This 10-item version of FiRST was tested in a multicenter study carried out at three multidisciplinary pain centers and three rheumatology departments with the aim of identifying the combination of items with the best discriminative value for distinguishing between FMS and three other frequent non-FMS (NFMS) rheumatological disorders associated with chronic diffuse pain: rheumatoid arthritis (RA), diffuse (i.e. more than three joints involved) osteoarthritis (OA) and ankylosing spondylitis (AS). Finally, 6 items were retained for the final questionnaire. |
| 1. RELIABILITY | |
| A. Internal Consistency | Tested |
| Cronbach's (Describe) |
Cronbach’s alpha coefficient was 0.66. |
| B. Reliability intraobserver or test-retest | Tested |
| Continuous scores: intraclass correlation coefficient (ICC) Dichotomus: Cohen kappa (Describe) |
The test–retest reliability of the total score of the questionnaire was assessed 7 ± 1 days after the first visit. The ICC of the FiRST total score was 0.87.. In another study, Fleiss' Kappa, Gwet's AC1 and percentage of agreement were also calculated between test and retest. AUC, Fleiss' Kappa, Gwet's AC1 and percentage of agreement were, respectively, 0.82, 0.38, 0.63 and 71.8%. |
| C. Reliability interobserver or Measurement error | Not Tested |
| Standard error of measurement (SEM), smallest detectable change (SDC) or Limits of agreement (LoA) (Describe) |
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| 2. VALIDITY | |
| A. Content validity: face validity | Tested |
| Expert opinion (relevance and comprehensiveness) (Describe) |
Patients were asked to rate (‘bad’, ‘moderate’, ‘good’) the quality of each item of the questionnaire, in terms of the clarity of wording, presentation and clinical relevance. The wording and clinical relevance of the items included in the questionnaire were considered ‘‘good” or ‘‘very good” by the vast majority (>95%) of the patients. Six experts (who were not members of the advisory committee) were asked to rate (bad, moderate, good, very good), independently, the extent to which each item of the final version was representative of the most relevant clinical characteristics of FMS. The six FMS experts concluded independently that the items included in FiRST were representative of the clinical features of FMS. |
| B. Construct Validity: Structural validity |
Not Tested |
| Hypotheses-testing | Tested |
| Cross-cultural validity | Tested |
| Brief Description | |
| C. Criterion validity | Tested |
| Comparison with a 'gold standard' Continuous scores: correlations, ROC curves Dichotomus: Sensitivity & Specificity (Describe) |
For each item, the proportion of ‘‘yes” responses was compared between the FMS patients and NFMS patients, using a chi2 test. The cut-off value for diagnosis was determined on the basis of the percent of FMS patients correctly identified, sensitivity, specificity and Youden index. A cut-off score of 5 resulted in the highest proportion of correctly identified patients (87.9%), and had a sensitivity of 90.5% and a specificity of 85.7%. The ROC curve plotted for the FiRST total score showed an AUC of 0.93. |