Original articleDetecting and monitoring depression with a two-item questionnaire (PHQ-2)
Introduction
With the lifetime prevalence of major depressive disorder being as high as 16% and appropriate treatment rates being as low as 22% [1], improving depression diagnosis, follow-up, and treatment remains a health care priority, especially in the general medical setting. The U.S. Preventive Task Force recently provided evidence-based recommendations regarding screening adults for depression in clinical practices that have systems in place to assure accurate diagnosis, effective treatment, and follow-up [2]. In research, depression is frequently measured as a primary or secondary outcome. Due to its effects on adherence, disability, and mortality, depression also is a potential confounder that needs to be controlled for in many clinical trials.
Brief self-report questionnaires have been advocated for depression screening in primary care [2]. Although multiple studies have shown that available depression screeners are generally comparable [3], [4], [5], recent work has suggested that the nine-item depression scale of the Patient Health Questionnaire (PHQ-9; [6], [7]) may have superior operating characteristics relative to several other depression screeners [8], [9]. Similarly, superior operating characteristics have been established for the panic module of the PHQ [10]. Another strength of the PHQ-9 is its proven sensitivity to change [11], [12]. Finally, PHQ diagnostic algorithms are not overinclusive but result in realistic estimates of base rates for depressive disorders [13].
Nevertheless, in clinical practice, as well as in research, depression is often not the only condition that needs to be screened for. Consequently, even shorter measures may be desirable. The initial evidence that two items might be sufficient for depression screening was provided for the two items on depressed mood and loss of interest from the Primary Care Evaluation of Mental Disorders (PRIME-MD) Screening Questionnaire [4], [14]. These findings were recently replicated for the same two items asked verbally by general practitioners [15]. However, due to its dichotomous (yes/no) response format, this screener is not suitable for grading depression severity or for assessing depression change over time. A measure that might overcome these shortcomings is the two-item PHQ (PHQ-2; see Appendix A), which has a four-point response format for each of its two items, with total scores ranging from 0 to 6 [16]. The only PHQ-2 validation study so far used the PRIME-MD as the criterion standard for depressive disorders [16]. However, as the PRIME-MD includes the two items of the PHQ-2, both measures are not completely independent. Thus, comparison with an independent diagnostic interview would strengthen the diagnostic validity of the PHQ-2. In addition, it remains uncertain how strongly PHQ-2 scores correlate with scores from longer depression self-report scales. Finally, sensitivity to change of the PHQ-2 has not yet been established, which is a precondition if the PHQ-2 is to be used to assess depression outcome.
Therefore, this study investigated the psychometric characteristics of the PHQ-2 as a brief measure for depression diagnosis and follow-up. Specifically, the reliability, construct and criterion validity, and sensitivity to change of the PHQ-2 were evaluated.
Section snippets
Participants
First, to investigate the validity of the PHQ-2 with respect to an independent diagnostic interview and established depression scales, data from a cross-sectional study were analyzed. Second, to assess sensitivity to change of the PHQ-2, results from a 1-year follow-up study were used, which included a predefined subgroup of patients from the cross-sectional study. Both studies were also instrumental in establishing the criterion validity and sensitivity to change of the PHQ-9 [8], [11]. Thus,
Patient characteristics
The baseline characteristics of the participants participating in the cross-sectional study are summarized in Table 1. In the total sample, mean age was 43.4 years, with 63.6% being female. At baseline, major depressive disorder, as diagnosed with the SCID, was present in 71 (13.6%) patients, and 132 (25.4%) patients were diagnosed as having any depressive disorder. The most common physical diagnoses according to ICD-10 were diseases of the musculoskeletal system and connective tissue (21%),
Discussion
Our study findings suggest that the PHQ-2 is not only a practical but also a valid tool to assess depression diagnosis, severity, and outcome. Comprehensive assessment established the reliability, construct and criterion validity, and sensitivity to change of the PHQ-2. Comparison with the seven-item HADS and the WBI-5 revealed that the PHQ-2 is evenly matched with longer depression screeners. The strong association of the PHQ-2 score with depression scores of three other questionnaires, the
Acknowledgments
This paper was supported by a research award from the Max-Kade Foundation, New York, to Dr. Löwe. The German version of the PHQ was originally developed with an unrestricted grant from Pfizer, Germany, and an additional research grant from the medical faculty of the University of Heidelberg, Germany (Project 121/2000). There are no conflicts of interest in connection with this paper.
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