Effects of education, literacy, and dementia on the Clock Drawing Test performance

The Clock Drawing Test (CDT) has been recognized as an effective tool for dementia detection. This study investigated the clock drawing performance of 240 non-demented elderly Korean people with a wide-range of educational levels and 28 patients with mild dementia of the Alzheimer's type (DAT). We examined the effects of demographic factors, including education, and established norms for the elderly population. We found that the educational attainment and literacy status of older people influenced performance on the CDT significantly (p < .001). Furthermore, qualitative error analysis revealed that normal participants with low educational background committed errors similar to errors of the DAT patients. The DAT patients performed significantly worse than the non-demented participants in the CDT Total score (p < .001). However, the CDT has better criterion validity in participants with more than 6 years of education. In conclusion, the CDT performance in older people who are either illiterate or with 6 or less years of education should be interpreted with caution. Conceptual errors in the CDT can be the result of not only dementia but also lack of education.