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