Psychometric Validation of the PHQ‐9 in Ostomy Patients and Their Informal Caregivers: Evidence From A European Multicenter Study

Introduction: Depressive symptoms are highly prevalent among individuals with an ostomy and their informal caregivers, negatively affecting quality of life and healthcare outcomes. Although the Patient Health Questionnaire-9 (PHQ-9) is widely used for depression screening, its psychometric properties have not previously been examined simultaneously in ostomy patients and their informal caregivers, limiting its applicability in this clinical context. Aim: To evaluate the validity, reliability and measurement invariance of the PHQ-9 in a European sample of ostomy patients and their informal caregivers. Method: This secondary analysis used data from a multicenter observational study including 523 ostomy patients (63.9% males, mean age 68.65 years) and 252 informal caregivers (80.6% females, mean age 58.7 years) recruited from outpatient clinics across Italy. Structural validity was examined using confirmatory factor analysis, comparing unidimensional and bidimensional models. Measurement invariance across patients and caregivers was assessed using multigroup confirmatory factor analysis. Internal consistency was assessed using omega coefficients and construct validity was tested through correlations with ostomy-specific and generic quality of life measures. Results: Confirmatory factor analysis supported a bidimensional structure of the PHQ-9, reflecting somatic and cognitive symptoms for both patients and caregivers, with excellent model fit. Internal consistency was adequate, with omega coefficients ranging from 0.71 to 0.88. Construct validity was supported by significant negative correlations between PHQ-9 scores and quality of life measures. Scalar measurement invariance was established, indicating the PHQ-9 functions equivalently in patients and caregivers. Conclusion: The PHQ-9 is a valid and reliable instrument for assessing depressive symptoms in patients with ostomy and their caregivers and can be confidently used for depression screening in both clinical and community care settings. Implications for the Profession and/or Patient Care: Its use in routine nursing practice can support early identification and management of depression in both clinical and community care contexts.