Psychometric evaluation of the Major Depression Inventory (MDI) as depression severity scale using the LEAD (Longitudinal Expert Assessment of All Data) as index of validity

Background: The Major Depression Inventory (MDI) was developed to cover the universe of depressive symptoms in DSM-IV major depression as well as in ICD-10 mild, moderate, and severe depression. The objective of this study was to evaluate the standardization of the MDI as a depression severity scale using the Visual Analogue Scale (VAS) as index of external validity in accordance with the LEAD approach (Longitudinal Expert Assessment of All Data). Methods: We used data from two previously published studies in which the patients had a MINI Neuropsychiatric Interview verified diagnosis of DSM-IV major depression. The conventional VAS scores for no, mild, moderate, and severe depression were used for the standardization of the MDI. Results: The inter-correlation for the MDI with the clinician ratings (VAS, MES, HAM-D17 and HAM-D6) increased over the rating weeks in terms of Pearson coefficients. After nine weeks of therapy the coefficient ranged from 0.74 to 0.83. Using the clinician-rated VAS depression severity scale, the conventional MDI cut-off scores for no or doubtful depression, and for mild, moderate and severe depression were confirmed. Conclusions: Using the VAS as index of external, clinical validity, the standardization of the MDI as a measure of depression severity was accepted, with an MDI cut-off score of 21 for mild depression, 26 for moderate depression severity, and 31 for severe depression.