The utility of the Edinburgh Depression Scale as a screening tool for depression in Parkinson’s disease Running head: Validity of the Edinburgh Depression Scale in PD Keywords: Parkinson’s disease, depression, Edinburgh Depression Scale, validity

Objective: This study aimed to evaluate the Edinburgh Depression Scale (EDS) as a screening tool for use in a Parkinson’s disease (PD) population. Many commonly-used depression scales include items relating to somatic symptoms that also occur in PD which could potentially result in inaccurate reporting of depressive symptoms. The EDS is a scale which incorporates no somatic items. Method: 120 patients attending specialist PD clinics were assessed using a standardized diagnostic interview (PSE-SCAN) to establish a diagnosis of DSM-IV depression. They later completed the EDS with another researcher who was blind to the results of diagnostic interview. A receiver operating characteristics curve analysis was carried out to identify the optimal threshold score on the EDS, and the Brief EDS, to identify any depressive disorder, or major depression. The performance characteristics at a range of thresholds were compared. Results: A cut-off score of 10/11 gave maximal discriminant validity, with 74% sensitivity, 92% specificity and 64% positive predictive value for the identification of any depression according to DSM-IV criteria. Conclusions: This study suggests the EDS is both a valid and potentially useful instrument which can be used as a quick self-completion questionnaire for screening for depression in people who have PD. Declaration of interest: None