Assessing the validity of the PHQ-9, HADS, BDI-II and QIDS-SR16 in measuring severity of depression in a UK sample of primary care patients with a diagnosis of depression: study protocol

Background: The 2004 NICE Guidelines and the Quality and Outcomes Framework (QOF) of the new General Medical Services (nGMS) emphasise the importance of measuring the severity of depression in primary care in order to target the condition with an appropriate intervention; however, there is an absence of UK objective psychometric comparisons between the endorsed measures (Patient Health Questionnaire (PHQ-9), Hospital Anxiety and Depression Scale (HADS) and Beck Depression Inventory (BDI-II)). Preliminary investigations on the HADS and PHQ-9 have demonstrated a lack of concordance between the measures' categorisation of severity of depression, leading to a lack of confidence in their validity in this respect.
Methods/Design: The present study proposes to assess the validity of the PHQ-9, HADS, BDI-II and Quick Inventory of Depressive Symptomatology (Self Report) (QIDS-SR16) in measuring severity of depression in a sample of primary care patients with a diagnosis of depression and to establish empirically derived severity cut-off scores for these measures. The aim is to recruit 500 patients from general practices across Grampian, Scotland. A full psychometric assessment will be undertaken including investigations of: reliability, factor structure, convergent/discriminant validity, responsiveness to change and empirical derivation of valid severity bandings.

Discussion: Presently the best method for measuring severity of depression in primary care is not known. The findings of this research will provide important information to general practitioners when considering how best to assess depression severity.