VALIDATION DATA

The overall internal consistency reliability of the PD-Q items by Cronbach’s alpha was > 0.83.

The test-retest stability of pain descriptors of the PD-Q within a time window of 1-3 weeks (mean 15 days), using data sets of 74 chronic pain patients sampled in an open pain register at two visits was calculated, revealing a Pearson correlation coefficient r was in the range of 0.72-0.86, intraclass correlation coefficient ICC was 0.71-0.86, and kappa was 0.62-0.72 for PD-Q pain descriptors.

In another study with patients with different rheumatic diseases, the test-retest revealed: ICC: RA 0.86(0.56–0.96), PsA 0.96(0.74–0.99), SpA 0.93(0.76–98), overall 0.94(0.84–0.98)

The level of patients’ acceptance of the PDA questionnaire was very high: 80% had no problems, 10% minor problems and only 10% required assistance.

The principal component analysis supported unidimensionality; thestandardized residuals showed that 53.7% of total variance was explained by the measure and the magnitude of firstcontrast had an eigenvalue of 1.5, no misfitting items, clinical insignificant different item hierarchies across diagnoses (DIF < 0.5 logits).

The electronic and paper version of the questionnaire demonstrated high criterion validity, compared to the reference standard of an expert pain physician, indicated by high sensitivity, specificity, and positive predictive value (all > 80%).