To evaluate the validity of the Beck Depression Inventory (BDI) as a screening and diagnostic scale for depression in Parkinson's disease (PD).
Fifty-three nondemented patients with PD were diagnosed according to a standardized protocol consisting of the depression module of the Structured Clinical Interview for DSM axis I disorders (SCID) and the BDI. A "receiver operating characteristics" (ROC) curve was obtained and the sensitivity, specificity, positive and negative predictive values (PPV and NPV, respectively) were calculated for different cut-off points of the BDI.
Maximum discrimination was obtained with a cut-off score of 13/14. High sensitivity and NPV were obtained with cut-off scores of 8/9 or lower; a high specificity and PPV were obtained with cut-off scores of 16/17 or higher. The area under the ROC curve was 85.67%.
A single cut-off score on the BDI to distinguish nondepressed from depressed patients with PD is not feasible. If one accepts the low specificity, then the BDI can be used as a valid screening instrument for depression in PD with a cut-off of 8/9. With a cut-off score of 16/17, it can be used as a diagnostic scale, at the cost of a low sensitivity. The use of diagnostic criteria for depression remains necessary.