Daily exposure to digital displays may affect the clock-drawing test: from psychometrics to serendipity

Background: The clock-drawing test (CDT) is a neuropsychological screening tool largely used to explore cognitive functioning. It requires participants to draw an analog clock face. Many studies have reported a good correlation between the CDT and the Mini-Mental State Examination (MMSE). The CDT has also showed a variable specificity. There are, however, some inconsistencies concerning the effect of sociodemographic variables (sex, age, education) on clock-drawing abilities. The present study aimed at examining these issues in a sample of middle-aged/young-old healthy adults. Method: Participants (n = 97) performed the MMSE and CDT. Clock drawings were assessed by five formal scoring systems (Wolf-Klein, Watson, Freedman, Manos, Shulman). In addition, three naïve raters provided a dichotomous judgment (normal vs. abnormal) for each clock. Results: Sociodemographic variables did not affect CDT performance. Unlike earlier studies, CDT scores did not correlate with MMSE. Moreover, test specificity was appropriate only for Freedman’s, Shulman’s, and Wolf-Klein’s methods. Interestingly, some participants drew clocks with numbers as they appear in digital clocks. By re-running the statistical analyses after removing these atypical clocks, four out of the five formal scores showed a significant correlation with MMSE; furthermore, CDT specificity slightly increased for all scoring systems including naïve ratings. Conclusions: CDT is not affected by sociodemographic variables. The finding of some clocks with digitally represented numbers suggests the need to align neuropsychological assessments with demands from an increasing digitalized environment. Moreover, the occurrence of high false-positives and possible digital contaminations suggest great caution in interpreting the clinical significance of CDT.