A reduced scoring system for the Clock Drawing Test using a population-based sample

Abstract

Many scoring systems exist for clock drawing task variants, which are common dementia screening measures, but all have been derived from clinical samples. This study evaluates and combines errors from two published scoring systems for the Clock Drawing Test (CDT), the Lessig and Tuokko methods, in order to create a simple yet optimal scoring procedure to screen for dementia using a Canadian population-based sample. Clock-drawings from 356 participants (80 with dementia, 276 healthy controls) from the Canadian Study on Health and Aging were analyzed using logistic regression and Receiver Operating Characteristic curves to determine a new, simplified, population-based CDT scoring system. The new Jouk scoring method was then compared to other commonly used systems (e.g. Shulman, Tuokko, Watson, Wolf-Klein). The Jouk scoring system reduced the Lessig system even further to include five critical errors: missing numbers, repeated numbers, number orientation, extra marks, and number distance, and produced a sensitivity of 81% and a specificity of 68% with a cut-off score of one error. With regard to other traditionally used scoring methods, the Jouk procedure had one of the most balanced sensitivities/specificities when using a population-based sample. The results from this study improve our current state of knowledge concerning the CDT by validating the simplified scoring system proposed by Lessig and her colleagues in a more representative sample to mimic conditions a general clinician or researcher will encounter when working among a wide-ranging population and not a dementia/memory clinic. The Jouk CDT scoring system provides further evidence in support of a simple and reliable dementia-screening tool that can be used by clinicians and researchers alike.