Validity and reliability of the Patient Health Questionnaire-8 in Swedish for individuals with systemic sclerosis
Malin Mattsson, Gunnel Sandqvist, Roger Hesselstrand, Annica Nordin, Carina Boström
Abstract
Abstract Background Depressive symptoms are common in rheumatic diseases and influence patients’ quality of life. The Patient Health Questionnaire-9 (PHQ-9), which assesses symptoms of depression, is valid in English in patients with systemic sclerosis (SSc). However, the measurement properties of the PHQ-8 (short version of the PHQ-9) have not been evaluated in Swedish patients with SSc. Objective To investigate different aspects of validity and reliability of the PHQ-8 in Swedish (PHQ-8 Swe) for individuals with SSc. Methods A total of 101 patients with SSc participated. Content validity was evaluated via interviews of 11 patients and 10 health professionals. Construct validity, internal consistency test–retest reliability, and floor/ceiling effects were evaluated in 90 patients. Results Content validity was satisfactory, but some linguistic adjustments were made. Confirmatory factor analysis supported a better fit for a two-factor structure. Moderate-to-strong correlations were found between the PHQ-8 Swe and scleroderma HAQ including VAS ( r s = 0.4–0.7); Multidimensional Assessment of Fatigue ( r s = 0.7); RAND-36 subscales ( r s = − 0.5 to − 0.8); and lung disease severity (Medsger scores) ( r s = 0.4). There were weak correlations ( r s = <0.4) between the PHQ-8 Swe and modified Rodnan skin score; and vascular, heart, and kidney disease severity. Cronbach’s alpha was 0.85, corrected item-to-total correlations were >0.40, and the ICC for the total score was 0.83. No floor/ceiling effects were found. Conclusion The PHQ-8 Swe has satisfactory content validity and sufficient reliability in patients with in majority limited SSc. It is more strongly associated with self-reported disability, pain, disease interferences with daily activities, fatigue, and quality of life than with disease severity, except for a moderate association with lung severity.