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

The study did not compare PHQ-9 scores with a gold-standard depression diagnosis, so it cannot establish diagnostic accuracy or optimal cut-offs. Participants were from outpatient ostomy clinics in Italy and mostly had low depressive symptoms, so the findings may not apply to inpatients, psychiatric services, or other countries. The design was cross-sectional, so it does not show whether PHQ-9 scores are stable over time or sensitive to change. Many PHQ-9 items had floor effects because few participants reported severe symptoms, which can reduce the scale's ability to distinguish between people with low symptom levels. Although patient and caregiver data were paired, the main psychometric analyses treated them as separate individuals and did not formally model the dyad.

This work was funded by the Centre of Excellence for Nursing Scholarship and Lega Italiana Lotta contro I Tumori. The authors declared no conflicts of interest.

Do not treat the PHQ-9 as a diagnostic test for depression. The study validated the questionnaire in Italian outpatient ostomy patients and caregivers, mostly with low symptom severity, and did not compare it with a clinical interview. Do not use the physical and mental symptom groups as separate clinical subscales.