Applicability and validity of the Major Depression Inventory in patients with Parkinson's disease

Since depressive symptoms in patients with Parkinson's disease (PD) fluctuate greatly, two depression questionnaires measuring frequency of symptoms rather than intensity were analyzed in 89 PD patients. Both scales (Zung-SDS and Major Depression Inventory (MDI)) were analyzed for internal validity by means of coefficients of homogeneity and factor analysis. The results showed that the MDI was superior to the Zung-SDS when measuring the dimension of severity of depression in terms of both homogeneity coefficients and factor analysis. The intercorrelation between the two scales was 0.75 (Spearman coefficient). When the scores of MDI were used for diagnosing depression, 11% of the patients had moderate depression by the ICD-IO and 13% of the patients had major depression by the DSM-IV.