Brief assessment of depression: Psychometric properties of the Portuguese version of the Patient Health Questionnaire (PHQ-9)
Authors: Ferreira Tiago , Sousa Marlene , Salgado João 
Published: December 2019

Background: The lack of knowledge regarding psychometric characteristics of brief scales for assessing the severity of symptoms of depression for the Portuguese population limits the ability of health professionals to signal clinically relevant situations, as well as the implementation of alternative forms of mental health care. The Patient Health Questionnaire (PHQ-9) is a scale whose usefulness in various professional contexts has been amply demonstrated by research. However, some of its psychometric qualities remain unknown for the Portuguese version.Goals: The main objective of this study was to analyse the validity of the factorial structure and the psychometric characteristics of the PHQ-9 in two different clinical Portuguese contexts, namely in primary health care units and in a university clinic, also reflecting the similarities and differences found regarding the factorial structures.Methods: The first study was carried out with 153 patients (83.66% females), with a mean age of 46.10 years (SD = 16.79), from eight health units of primary health care (non-probabilistic sampling). All participants underwent an initial screening for the detection of symptoms of depression and suicidal ideation, within the context of a regular family medicine appointment or nursing visit. Participants who scored positively for one of these symptoms were invited to participate in the study. The PHQ-9 and the Work and Social Adjustment Scale (WSAS) were used and exploratory and semi-confirmatory factor analyses of the PHQ-9 were performed. In the second study, 106 adults (70.78% females) participated in a psychological counselling session at a university clinic, with a mean age of 32.47 years (SD = 11.01), also constituting a non-probabilistic sample. As instruments, the PHQ-9, the Beck-II Depression Inventory and the State-Trait Anxiety Inventory were used, which participants completed before the beginning of the psychological treatment. As in the first study, exploratory and semi-confirmatory factor analyses of the PHQ-9 were conducted. Results: The results of the two studies revealed a factorial structure consisting of three factors. In the first study, the three factors were: (1) depressed mood and anhedonia; (2) self-devaluation and suicidal ideation; and (3) fatigue, psychomotor agitation/retardation, and changes in appetite, sleep problems or difficulty in concentration. In the second study, the three factors that were found were: (1) sleep problems and fatigue; (2) changes in appetite and difficulty in concentration, psychomotor agitation/retardation, and suicidal ideation; and (3) depressed mood, anhedonia, and self-devaluation. The factorial structure found in both studies revealed a good fit. The PHQ-9 also presented good internal consistency, convergent validity and criterion validity in both studies. The cut-off point of 9 emerged as an indicator of major depression.Discussion: The results of this study enhance the use of this scale in different contexts of health care provision in Portugal, since it was possible to determine the cut-off point for the detection of cases with major depression, as well as the criteria for delimiting severity degrees of depression-related symptomatology.Keywords: PHQ-9, Depression, Psychometric qualities, Primary health care, University clinic