Establishing the cut-off score for remission and severity-ranges on the Psychotic Depression Assessment Scale (PDAS).

Background: The Psychotic Depression Assessment Scale (PDAS) is a rating scale dedicated to the measurement of severity in psychotic depression (PD). The aim of this study was to establish the PDAS cut-off for remission of PD as well as PDAS score-ranges for mild, moderate, and severe PD. The secondary aim was to test how remission, as defined by the PDAS, would perform as outcome measure when applied to the data from a large randomized controlled trial (RCT) in PD.
Methods: The study was based on data from the Study of Pharmacotherapy in Psychotic Depression (STOP-PD). The cut-off for remission on the PDAS and the severity-ranges for mild, moderate, and severe PD were defined using the Clinical Global Impression - Severity scale (CGI-S) as reference by means of pair-wise receiver operating characteristic (ROC) analyses. Subsequently, it was tested whether remission on the PDAS could separate the effects of Olanzapine+Sertraline vs. Olanzapine+Placebo through an intention-to-treat, mixed-effects logistic regression of the data from STOP-PD.
Results: According to the ROC analyses, the ideal cut-off for remission of PD was a PDAS total score <8, while the severity-ranges for mild, moderate and severe PD were 8-15, 16-23, and >23 respectively. When applying the PDAS total score <8 (remission) as outcome on the STOP-PD data, treatment with Olanzapine+Sertraline performed significantly better than Olanzapine+Placebo (p<0.001).
Limitations: The STOP-PD was not designed specifically to answer the research questions of the present study.
Conclusions: According to this study, a total score <8 on the PDAS corresponds to remission of PD.
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