As the name implies, the PDAS was constructed specifically to assess the severity of psychotic depression (PD). The scale was developed through analysis of item-level ratings on the 17-item Hamilton depression rating scale (HAM-D17) and the Brief Psychiatric Rating Scale (BPR)S from the Study of Pharmacotherapy of Psychotic Depression (STOP-PD), which represents the largest randomized controlled trial ever carried out in PD. The PDAS consists of 11 items, the 6-item melancholia subscale (HAM-D6), derived from the HAM-D17, plus five psychosis items from the BPRS. The 11 items are: depressed mood, guilt feelings, work and activities, psychomotor retardation, psychic anxiety and somatic symptoms (general) from the HAM-D6 and hallucinatory behavior, unusual thought content (delusions), suspiciousness, emotional withdrawal and blunted affect from the BPRS. Due to this fusion of core items from the HAM-D17 and the BPRS, the PDAS covers both of the main psychopathological domains of PD.