The validity and reliability of the Swedish version of the Satisfaction with appearance scale for individuals with systemic sclerosis

Abstract

Background: Systemic sclerosis (SSc) can lead to visible changes in appearance which could generate concerns among patients. Thus, valid questionnaires that capture these concerns are valuable to identify and communicate appearance concerns. Objective: To determine aspects of the validity and reliability of the Swedish version of the Satisfaction with Appearance scale for individuals with SSc (SWAP-Swe in SSc). Methods: Content validity was assessed by interviews. In a cross-sectional design, construct validity was evaluated by comparing the self-reported questionnaire SWAP-Swe in SSc to the Scleroderma Health Assessment Questionnaire (SSc HAQ), Patient Health Questionnaire-8 (PHQ-8), RAND-36, modified Rodnan skin score (mRSS), disease duration and age using Spearman’s rank correlations ( rs). Internal consistency was evaluated by Cronbach’s alpha coefficient and corrected item-to-total correlations. Test–retest reliability was investigated using the intraclass correlation coefficient (ICC). Results: Eleven patients and 10 health professionals participated in the assessment of content validity. For the other aspects of validity and reliability 134 patients (median age 62 years, women 81%, limited cutaneous SSc 75%) participated. Overall, the content validity was satisfactory. The SWAP-Swe in SSc correlated with SSc HAQ (HAQ-DI rs = 0.50, visual analogue scales rs = 0.24–0.41), PHQ-8 ( rs = 0.46), RAND-36 ( rs = −0.21 to −0.47), mRSS ( rs = 0.28), disease duration ( rs = −0.01) and age ( rs = −0.15). The Cronbach’s alpha coefficient was 0.92, corrected item-to-total correlations ⩾ 0.45 and the ICC 0.82. Conclusion: The SWAP-Swe in SSc showed satisfactory content validity, sufficient and good internal consistency and sufficient test–retest reliability. It was more strongly associated with self-reported questionnaires than with physician-assessed skin involvement and age, indicating that appearance concerns in SSc seem to be multidimensional as earlier reported. Our study contributes with a thorough investigation of validity and reliability including aspects that have not been investigated before. However, evaluation of more validity aspects of the SWAP-Swe in SSc is suggested.