Influence of established and subjectively perceived as well as evaluated individual characteristics on the utilization of mental health services among individuals with depressive disorders: protocol of a longitudinal study examining how to supplement the "behavioral model of health services use" and on need-congruent use of mental health services.

BACKGROUND: Approximately one out of every three people in Germany who meets the diagnostic criteria for major depression has contact with mental health services. Therefore, according to treatment guidelines, two thirds of all individuals with depression are insufficiently treated. In the past, the subjective perspective of people who (do not) make use of mental health services has been neglected. Factors related to the use of health services are described in Andersen's Behavioral Model of Health Services Use (ABM). The aim of this study is to supplement operationalizations of subjectively perceived and evaluated individual characteristics in the ABM and to evaluate whether the supplemented model can better explain mental health services use in individuals with depression than established operationalizations.
METHODS: A representative telephone study with two measurement points will be conducted. In an explanatory mixed-methods design, qualitative interviews will be added to further interpret the quantitative data. A nationwide sample scoring 5 or more on the Patient Health Questionnaire (PHQ-9) will be recruited and interviewed via telephone at T0 and 12 months later (T1). Data on established and subjective characteristics as well as mental health service use will be collected. At T1, conducting a diagnostic interview (Composite International Diagnostic Interview, DIA-X-12/M-CIDI) enables the recording of 12-month diagnoses according to DSM-IV-TR criteria. Ideally, n = 768 datasets will be available and analyzed descriptively by means of regression analysis. Up to n = 32 persons who use or do not use depression-specific health services incongruent with their objective or subjective needs will be interviewed (face-to-face) to better explain their behavior. In addition, theories of non-need-based mental health service use are developed within the framework of the grounded theory-based analysis of the qualitative interviews. DISCUSSION: The study intends to contribute to the theoretical foundation of health services research and to specify the characteristics described in the ABM. Thus, after completion of the study, a further sophisticated and empirically tested model will be available to explain mental health services. The identified modifiable influencing factors are relevant for the development of strategies to increase mental health service use in line with the objective and subjective needs of individuals with depression.