VALIDATION DATA

Available in English, Turkish and Brazilian Portuguese

Kuder-Richardson Formula 20 (KR-20):0.95

Two-week interval postal questionnaire: Spearman’s rho 0.84

Analysis of the AS-WIS and AS Qaulity of Life scores for the respondents in work showed a correlation of 0.84 (Sperman’s rho) showing that 72% of the variation in Quality of life of those is associated with their level of WI.

Qualitative interviews; 1st Postal questionnaire; Final item reduction; 2nd Postal questionnaire

AS-WIS is a simple 20 item questionnaire to measure Work Instability in AS. In the final scale half the items where shared with the original RA-WIS providing evidence of the communality of some aspects of WI, but also the unique elements brought to the concept by each diagnostic group.

Item-trait interaction χ²: 24.8; DF 20; p=0.21

The scale showed good fit to Rash model expectations and satisfied the test for unidimensionality (independent t test 10.8% 95% CI 5-17%).

The targeting of the scale was good, with a mean person estimate of 0.033 logits SD 2.315, suggesting the scale to be centered on the person distribution.

Tested by Fabreguet et al (Rheumatology 2011), non-parametric Spearman's correlations.

Correlations of the AS-WIS score with SpA scores were significant (P < 0.0001) but moderate:

BASDAI R = 0.42,

BASFI R = 0.41,

Patient's global assessment R = 0.53;