Normative Norwegian scores on the clock drawing test using the Shulman version

Background Studies have shown that the performance on the Clock Drawing Test (CDT) is influenced by age and education. Thus, normative scores are needed. Objective To develop normative Norwegian scores for Shulman's version of CDT. Methods Performance on CDT of 2572 cognitively healthy people between age 25 and 95 years were included. Ordinal regression analysis was used to derive regression-based norms with sex, age and education as covariates. Results Of all, 76.4% scored five, 12.9% scored four, 8.1% scored three and 2.5% scored zero to two. Men scored higher than women. An interaction between age and education was found. The probability of higher CDT score is highest at younger ages and among those with highest education. It progressively declines with increasing age, while higher education delays, but does not prevent this decline. Participants scoring zero to two fell below the 5 th percentile, except among women above 93 years and men above 85 years. By age 95, the probability of different scores converged. In the age range of 60 to 90 years a score of three corresponded to percentiles of 3.7–26.9 in men and 5.2–34.1 in women, while a score of four corresponded to percentiles of 9.7–50.4 in men and 13.2–59.0 in women. Conclusions Scores four and five are considered normal for any person aged 60–90 years. Whether a score of three is normal depends on the person's sex, age and educational level, whereas score zero to two should not be regarded as normal.