VALIDATION DATA

Cronbach’s α = 0.99.

The consistency of the ratings of worst severity for the fatigue items in the long form between 0 and 24 hours appeared to be slightly lower for RA, with correlation coefficients of 0.52 to 0.72, than for the other two conditions (SLE: 0.69-0.89; pSS: 0.67-0.79) and healthy controls (0.64-0.81). 

The rated severity of the problem at worst was greater on average at 24 hours than 0 hours for all the fatigue terms. The repeatability over a 24-hour period of each of the three grouped symptom severity ratings in the domain of ocular dryness in the PROFAD-SSI-SF was high in each diagnostic group, with mean (+SD) percentage correlation coefficients of 92 (+2) in pSS, 91 (+5) in SLE, and 90 (+11) in RA, but was somewhat lower in controls (84 (+15)). Also, in oral dryness, the rated severity of the four grouped symptoms was consistent over 24 hours in all groups. The repeatability over 24 hours of the severity of a grouping of all the symptoms of systemic discomfort and/or arthralgia was high in all groups except RA, with mean percentage correlation coefficients of 92 in pSS, 94 in SLE, 79 in RA, and 92 in healthy controls. 

The PROFAD-SSI-SF was initially validated in a multicenter (12 participating sites) UK cohort that included 130 patients with pSS, 93 patients with SLE, 83 patients with RA, and 103 health community controls . The aim of these studies was to evaluate psychometric properties (construct validity, responsiveness, and reliability) and compare them with those of the Medical Outcomes Study 36-item Short Form Survey (MOS SF-36) and World Health Organization Quality of Life–Brief Version (WHOQoL BREV) questionnaires. All scores had an excellent reliability.

Factor analysis confirmed the previous domain structure. Spearman’s correlation between the domains of the long and short forms was between 0.779 and 0.996.