Development and psychometric evaluation of a questionnaire for the assessment of depression in primary care: a cross-sectional study

Abstract

Objectives To develop a new questionnaire for the diagnostic assessment of depression adapted to the primary care setting by combining psychiatric criteria and heuristics of general practitioners (GPs). Psychometric evaluation of the new questionnaire and first validity evidence.Design The questionnaire was developed using cognitive interviews with think-aloud technique. Factorial validity was then examined in a cross-sectional study.Setting Primary care. Five general practices in Bavaria, Germany.Participants 15 GPs, 4 psychiatrists/psychotherapists and 13 patients participated in cognitive expert interviews. A primary care sample of N=277 consecutive patients participated in the cross-sectional study.Methods After consultation with experts and literature research, the questionnaire contained a self-rating part for patients and an external part for GPs. Items were then iteratively optimised using cognitive interviews. Factorial validity was examined. To estimate internal consistency, Cronbach’s α was calculated. Validity was assessed by correlating the new questionnaire and the Patient Health Questionnaire-9 (PHQ-9).Results The preliminary version of the two-part ‘Questionnaire for the assessment of DEpression SYmptoms in Primary Care’ (DESY-PC) comprised 52 items for patients (DESY-PAT-1: questions about patient’s environment; DESY-PAT-2: questions about depression-specific symptoms) and 21 items for GPs (DESY-GP). The analysis of the DESY-PAT-1 revealed a one-factor solution (‘environmental factors’) with Cronbach’s α of 0.55. The items of the DESY-PAT-2 were assigned to three factors, ‘depressive cognitions’, ‘suicidality’ and ‘symptoms of fatigue’, with Cronbach’s α of 0.86, 0.79 and 0.85, respectively. Factorial analysis revealed two factors for the DESY-GP: ‘depression symptoms’ and ‘medical history/external factors’. Cronbach’s α was 0.90 and 0.59, respectively. After factorial analysis, the DESY-PAT was reduced to 28 items, and the DESY-GP was reduced to 15 items. Correlations of the DESY-PC with the PHQ-9 were high and significant, indicating convergent validity.Conclusions The new questionnaire represents an innovative extension of depression questionnaires and could be particularly suitable for general practices.