Diagnosing depression in primary care: a Rasch analysis of the Major Depression Inventory

Area of Science:

• Psychiatry
• Psychometrics
• General Practice Research

Background:

• The Major Depression Inventory (MDI) is a widely used tool for depression screening, diagnosis, and monitoring in primary care settings.
• Assessing the psychometric properties of diagnostic instruments is crucial for ensuring accurate patient assessment and effective treatment planning.

Purpose of the Study:

• To evaluate the measurement properties of the Major Depression Inventory (MDI) using Rasch analysis in a clinical sample of primary care patients.
• To determine the validity and reliability of the MDI for depression identification in adults attending general practice.

Main Methods:

• Rasch analysis was employed to assess the overall fit, item fit, person fit, and response category adequacy of the MDI.
• Statistical tests were conducted for local dependency, unidimensionality, differential item functioning, and scale targeting.
• The person separation reliability index was calculated using RUMM2030 software.

Main Results:

• Items 9 and 10 of the MDI showed misfit to the Rasch model, and initial analysis revealed disordered response categories for all items.
• Modifying the MDI's scoring from a six-point to a five-point system resulted in ordered response categories for all 10 items.
• The MDI demonstrated good targeting and model fit for core depression symptoms and when items were dichotomized.

Conclusions:

• Despite minor issues with its measurement structure, the MDI is considered a valid instrument for identifying depression in primary care adults.
• The findings support the use of MDI core symptoms and dichotomized items for depression screening and diagnosis.
• Future revisions of the MDI should address the identified measurement structure problems.