Reliability and validity of the Chinese version of the Patient Health Questionnaire-9 (C-PHQ-9) in patients with psoriasis: a cross-sectional study

Objective To evaluate the clinical reliability and validity of the Chinese version of the Patient Health Questionnaire-9 (C-PHQ-9) in patients with psoriasis. Design Cross-sectional study. Setting Tertiary care centre. Participants Patients with psoriasis who have not been diagnosed with depression (n=148; mean age 43.37 +/- 17.46 years; 31.19% female). Primary and secondary outcome measures The primary outcome measures considered in this study were the C-PHQ-9 and the Hamilton Depression Scale (HAMD). The American Diagnostic and Statistical Manual of Mental Disorders Fifth Edition (DSM-V) was used as the gold standard for the diagnosis of depression. Cronbach's alpha and test-retest reliability after 1 week were evaluated using reliability analysis, and criterion and structural validity were assessed using validity analysis. Receiver operating characteristic (ROC) analysis was performed to identify the best demarcation score and diagnostic accuracy. Results Compared with DSM-V (27.27%), both C-PHQ-9 (39.19%) and HAMD (31.01%) had higher rates for detecting depression. The mean completion time for C-PHQ-9 evaluation (2.02 +/- 0.84 min) was significantly less than that for HAMD (23.37 +/- 3.21 min, p<0.001). The Cronbach's alpha coefficient for the C-PHQ-9 was 0.938. The correlation coefficients of the nine items with the total scale ranged from 0.540 to 0.854, and the mean inter-item correlation coefficients ranged from 0.376 to 0.933. After a week, the retest coefficient was 0.955 (p<0.01). Principal component factor analysis showed that C-PHQ-9 identified a unifactorial structure. The best cut-off point was 9 points, with a sensitivity of 98.00% and a specificity of 90.80%. The area under the ROC curve was 0.979 (95% CI 0.968 to 0.991). Conclusion C-PHQ-9 has good reliability and validity in patients with psoriasis and can be used for primary screening of patients with psoriasis and depression. This scale has obvious time and labour advantages over the HAMD and should be considered for use in clinical practice.