In recent decades, several scales have been developed and validated to measure depression and have been used in clinical and non-clinical settings. One of the most widely used scales of depression in the last two decades is the Patient Health Questionnaire-9 (PHQ-9). This measure is used for screening depression in primary care [15]. One of the advantages of this tool is that it fully complies with the criteria for depression in the fourth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) [13]. In general, studies that have been conducted to validate PHQ-9 in different populations, medical settings, and different countries have shown that it has good psychometric properties and is a valid measure for evaluation of depressive symptoms. So far, four studies have been conducted to validate the PHQ-9 in Iran, using different target population, sample size, accompanied questionnaires, and methodology. Given the need for access to screening tools for depressive symptoms [9], the present study aimed to evaluate the psychometric properties of Persian version of PHQ-9 in the student population. We used a relatively large sample in order to increase the statistical robustness. We evaluated Convergent Validity (CV) and Discriminant Validity (DV) as well as test-retest reliability and internal consistency at the same time, and assessed the construct validity given the contradictory results of previous study [22] on the factor structure of PHQ-9.

This is a descriptive study. The study population included all students of Guilan University of Medical Sciences in the academic year 2018-19. Samples were selected using a convenience sampling method. After collecting data and excluding incomplete questionnaires, the final sample size was 463. To investigate the reliability of the Persian PHQ-9, both internal consistency and test-retest reliability for a 2-week interval were evaluated. Construct validity of PHQ-9 and its similarity or difference among the samples were evaluated using exploratory and confirmatory factor analyses. The CV and DV were also assessed by Pearson correlation test. To evaluate the convergent validity, the second version of the Beck Depression Inventory (BDI-II), the depression subscale of the 21-item Depression Anxiety Depression Inventory (DASS-21), the neuroticism subscale of NEO Five Factor Inventory (NEO-FFI) and the negative affect subscale of the Positive Affect and Negative Affect Scale (PANAS) were used. According to the study literature, these scales either measure the construct of depression or are in common with PHQ-9 in the basic construct of general psychopathology (neuroticism) and negative mood [9]. The openness subscale of NEO-FFI and the positive affect subscale of PANAS were also used to assess the discriminant validity. The positive affect subscale measures the reversed construct of depression. On the other hand, since people with low levels of openness are often prone to experience negative mood, openness is considered as the reversed construct of depression [9, 36]. In studies on the validation of other measures of depression, the above mentioned questionnaires have also been used to examine convergent validity and discriminant validity [9].

The Cronbach’s alpha coefficient of 0.856 and the intraclass correlation coefficient of 0.869 indicated the high test-retest reliability and internal consistency of the Persian PHQ-9, respectively. The Kaiser-Meyer-Olkin (KMO) value of 0.889 indicated that the sample size was adequate, and the results of Bartlett’s test of sphericity (Chi-square= 1468.31, df=36, P<0.0001) showed that the conditions for performing factor analysis were established. The results of exploratory factor analysis indicated that all items were in one factor (Range= 0.39-0.60, Eigenvalue= 4.28) and explained 47.95% of the total variance. The fitting indices of the one-factor model of the Persian PHQ-9 were reported as follows: Chi-square/Degree of Freedom =4.39 (P>0.05), Comparative Fit Index= 0.92, Non-Normed Fit Index= 0.90, Root Mean Square Error of Approximation= 0.03, and Standardized Root Mean Square Residual= 0.065. Standardized coefficients with a range of 0.063-0.68 showed that all items were related to one factor. Table 1 shows the results of CV and DV. Positive correlation of Persian PHQ-9 with BDI-II (r= 0.769), the neuroticism subscale of NEO-FFI (r= 0.508), the depression subscale of DASS-21 (r= 0.647) and the negative affect subscale of PANAS (r= 0.430) showed its acceptable CV, and its negative correlation with the positive affect subscale of PANAS (r= -0.444) indicated its acceptable DV, while it had no significant relationship with the openness subscale of NEO-FFI (r= 0.116)

The Persian PHQ-9 has acceptable validity and reliability to be used on Iranian student population. Our results can be compared with the findings of previous studies conducted on other countries on the student population [17, 25, 26, 51-54]. The results showed that the Persian version of PHQ-9 had high internal consistency and acceptable test-retest reliability. It had a positive correlation with the constructs of similar questionnaires and a negative correlation or non-correlation with the questionnaires having unrelated constructs. The construct validity assessment showed it the Persian PHQ-9 had a one-factor structure. The results of some studies conducted in other countries on the factor structure of PHQ-9 are somehow not consistent with our results. Some studies reported a single-factor structure [54, 55], while other studies found two- or three-factor structures with a diverse distribution of items in each factor [22, 53, 56]. Due to the consistence of our results with those of previous four studies [27-30] regarding the factor structure of the Persian version of PHQ-9, it can be concluded that it has one-dimensional construct validity to be used in various clinical and non-clinical settings in Iran. It has acceptable psychometric properties to be used on Iranian population, including the student population, and can be used as a short and easy-to-understand tool for screening, diagnosing and monitoring of the depression treatment outcome.

The study was approved by the Ethics Committee of Tehran University of Medical Sciences (Code: IR.IUMS.REC.1397.132). All ethical principles are considered in this article. The participants were informed about the purpose of the research and its implementation stages. They were also assured about the confidentiality of their information and were free to leave the study whenever they wished, and if desired, the research results would be available to them.

This study did not receive any specific grant from funding agencies in the public, commercial, or nonprofit sectors.

Conceptualization, research, editing, and finalization: All Authors; Methodology: Hassan Farhi, Banafsheh Gharaei and Roghayeh Zare; Data analysis, drafting: Hassan Farhi and Roghayeh Zare; Sources: Hassan Farhi; Supervision and coordination: Banafsheh Gharraee.

The authors declare no conflict of interest.
 

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