Impaired judgement' remains a diagnostic (and predictive) criterion for delirium, dementia and substance-related disorders, and yet its diagnosis and measurement are hampered by the absence of an operational definition. Most of the important research into judgement as a psychological function has been carried out in developmental and industrial psychology, in the experimental analysis of perception, medical diagnosis and legal decision-making. Models generated in these fields, although important, are only tangentially relevant to 'impaired judgement' as it is met with in clinical practice. This article explores some models of judgement and their application to dementia. It concludes that judgement is not a unitary function but a composite of subroutines. Hence, both low-and high-level analyses are required: the former to explore aetiology. differential diagnosis and treatment, the latter for the assessment of psychosocial competence. A model for the understanding of judgement is also suggested. KEY WORDS-Judgement; thinking; dementia 'Impaired judgement' has long been a diagnostic criterion for disorders such as delirium, dementia and substance abuse (ICD-10, DSM-111-R, CAMDEX). Although judgement is an important topic in developmental and decision-making psychology, management studies and medical diagnosis (Arkes and Hammond, 1986), little is known about the qualitative and quantitative aspects of this 'psychiatric symptom'. Interestingly enough, DSM-IV (American Psychiatric Association, 1994) has abandoned 'impairment of judgement' as a criterion for dementia, referring instead to 'disturbance in executive functioning' and 'the ability to think abstractly and to plan, initiate, sequence, monitor and stop complex behavior'. It remains to be seen whether the use of such a theory-driven notion will improve understanding. This article explores the relationship between 'impaired judgement' and dementia.
WHAT IS JUDGEMENT?
Judgement is derived from the French juger: 'to judge', which in turn comes from the Latin judico