CLOX: an executive clock drawing task
- aDepartment of Psychiatry, University of Texas, Health Science Center at San Antonio, Texas, USA, bDepartment of Medicine, South Texas Veterans’ Health System, Audie L Murphy Division, Geriatric Research Education Clinical Center (GRECC), cDivision of Clinical Pharmacology
- Associate Professor D R Royall, Department of Psychiatry, University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, Texas 78284–7792, USA. Telephone 001 210 567 8545; fax 001 210 567 8509; email:
- Received 11 April 1997
- Revised 29 July 1997
- Accepted 3 October 1997
OBJECTIVE To describe a clock drawing task (CLOX) designed to elicit executive impairment and discriminate it from non-executive constructional failure.
SUBJECTS 90 elderly subjects were studied (45 elderly and well persons from the independent living apartments of a continuing care retirement community and 45 patients with probable Alzheimer’s disease). The clock drawing performance of elderly patients was compared with that of 62 young adult controls.
METHODS Subjects received the CLOX, an executive test (EXIT25), and the mini mental state examination (MMSE). The CLOX is divided into an unprompted task that is sensitive to executive control (CLOX1) and a copied version that is not (CLOX2). Between rater reliability (27 subjects) was high for both subtests.
RESULTS In elderly subjects, CLOX subscores correlated strongly with cognitive severity (CLOX1:r=−0.83 v the EXIT25; CLOX2:r=0.85 v the MMSE). EXIT25 and MMSE scores predicted CLOX1 scores independently of age or education (F(4,82)=50.7, p<0.001;R 2=0.71). The EXIT25 accounted for 68% of CLOX1 variance. Only the MMSE significantly contributed to CLOX2 scores (F(4,72)= 57.2, p<0.001;R 2=0.74). CLOX subscales discriminated between patients with Alzheimer’s disease and elderly controls (83.1% of cases correctly classified; Wilkes’ lambda=0.48, p<0.001), and between Alzheimer’s disease subgroups with and without constructional impairment (91.9% of cases correctly classified; Wilkes’ lambda=0.31, p<0.001).
CONCLUSIONS The CLOX is an internally consistent measure that is easy to administer and displays good inter-rater reliability. It is strongly associated with cognitive test scores. The pattern of CLOX failures may discriminate clinical dementia subgroups.