The CORE was initially developed as a measure of the domains of psychomotor disturbance specific to melancholic and psychotic depressive disorders. A full description of its developmental is provided in Parker and Hadzi-Pavlovic (1996). The final measure comprises 18 signs (observable features) which are rated by the clinician or a trained observer at the end of a clinical interview. Each sign is rated on a 4-point scale (0–3), where a rating of 0 conveys a general concept of normality or the subject's usual behaviour. By contrast, a rating of 2 or 3 always implies definite pathological behaviour. A score of 3 also indicates severe disturbance on that behavioural domain. Sub-sets of items produce scores on each of three dimensions found to underlie psychomotor change: ‘non-interactiveness’, ‘retardation’, and ‘agitation’.

Principal components analysis of the 18 items of the CORE suggested a trunk and branch analogy for construing psychomotor disturbance and for deriving subscales. The six truncal items contribute to a non-interactiveness scale which is thought to reflect disturbances in neurocognitive processing or the psychic component of psychomotor disturbance, which, when severe, can generate a diagnosis of pseudo-dementia in depressed patients. The remaining CORE items on the left- and right-hand ‘branches’ define the motor aspects of psychomotor disturbance, with some specificity to either agitation or to retardation.