Validity of the Brief Patient Health Questionnaire Mood Scale (PHQ-9) in the general population
Introduction
Depressive disorders are fairly prevalent conditions in the general population and especially in primary care and general hospital settings. Depression is associated with severe impairment in physical, social and role functioning, and with higher health care utilization [1], [2]. Depressive symptoms are frequent coexisting problems in many medical illnesses and have been found to increase the risk of mortality and morbidity, such as in coronary heart diseases [3], [4]. On the other hand, patients suffering from depressive disorders often do not seek help for psychological problems, but instead present somatic symptoms to their physicians, and their depression often goes unrecognized [5], [6]. According to the WHO Psychological Problems in General Health Care study, only 42% of primary care patients with major depression were recognized by the physician [7]. Therefore it has been emphasized that it is a key challenge in the health care system to identify depressive disorders early. Screening questionnaires have been advocated as an aid to the detection of cases and clinical decision making.
Previous self-report instruments used for case finding or screening of mental disorders yield indices of severity rather than categorical psychiatric diagnoses. The Patient Health Questionnaire (PHQ) is based on DSM-IV criteria, its disorders divided into threshold disorders according to DSM-IV and subthreshold conditions. It has been developed as a fully self-administered version of the original PRIME-MD by Spitzer et al. [8]. PRIME-MD is a two-stage system consisting of a patient-screening questionnaire and the clinician evaluation guide to detect the most common groups of mental disorders in primary care. The two components of the original PRIME-MD instruments were combined in a self-report questionnaire. Two versions are available: the PHQ with the complete diagnostic part (four pages) and the Brief-PHQ (two pages) covering mood and panic disorders.
The PHQ has already been studied in different medical settings, e.g., in primary care patients [8], [9], in general hospital inpatients [10] and in obstetrics-gynecological patients [11]. Among 3000 primary care patients, a prevalence rate of 28% of any mental disorder and 10% with major depression and 6% with other depressive disorders was reported [8]. The German version of the PHQ depression module (PHQ-9) has been validated twice in primary care settings: Henkel et al. [9] determined a sensitivity of 78% and a specificity of 85% in the depression module, with specificity and positive predictive value to be better than in the other screening questionnaires GHQ-12 and WHO-5. Löwe et al. [12] reported the PHQ's operating characteristics for major depression to be significantly superior to two other screening instruments (WBI-5 and HADS). Aspects of convergent validity of the PHQ have also been reported in previous studies conducted in medical settings, showing strong associations between PHQ psychiatric diagnosis and functional impairment as well as disability days [8], [11]. Further, strong associations of the PHQ-9 depression severity score as a continuous variable with the different aspects of health-related quality of life (SF-20) were found [13]. In sum, these results supply strong evidence for the PHQ as a valid screening instrument in medical settings. Validity of the PHQ in the general population is unknown.
Therefore the main subject of the present study was to assess aspects of construct validity of the PHQ-9 in a population-based sample. To compare the PHQ-9 with convergent variables, two screening instruments were chosen to assess psychological distress (GHQ-12) and depression (Brief-BDI). In addition, the relation of diagnostic results of the PHQ-9 to subjective health perception and health-related quality of life was assessed.
We hypothesized that the PHQ-9 diagnostic groups would have different scores on these clinical variables, with lowest disability scores in the DS− and highest scores in the two depressive groups (major depression and other depressive disorder). Further, we expected strong associations between depression severity and the other variables assessing depression, psychological distress, general health and disability.
Section snippets
Subjects
A representative sample of the general population of Germany was selected with the assistance of a demography consulting company (USUMA, Berlin). The sample selection was based on the political election register in 1998, and 201 sample points were used. The sample was selected to be representative in terms of age, gender and education. Inclusion criteria were age above 13 years and German as a native language. A first attempt was made for 3194 addresses following a random-route procedure. The
Diagnostic results
Table 1 presents the prevalence of mood disorders and panic syndrome diagnosed by the Brief-PHQ in the representative sample (n=2060; in six cases diagnostic information was incomplete/missing). Nearly 10% of the subjects (n=204) had at least one of the possible diagnoses. The majority of these subjects fulfilled the criteria of a current mood disorder: 3.8% having major depression and 5.4% having the subthreshold diagnosis of any other depressive disorder. Only 1.9% fulfilled the criteria of
Discussion
The main aim of this study was to assess the construct validity of the PHQ depression scale PHQ-9 in the general population. While there is already a body of evidence that supports its validity in medical settings [8], [10], [11], no data are available on its validity in the general population. The diagnoses of the PHQ-9 are based on the criteria for major depression according to DSM-IV [24]. An advantage of a screening instrument based on these operational definitions of mental disorders is
Acknowledgment
This study was supported by grants from the German Ministry of Education and Research BMBF and from Pfizer Germany, Karlsruhe. The first author has previously published with the surname “Nanke.”
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