Comparing the Influences of Age and Disease on Distortion in the Clock Drawing Test in Japanese Patients With Schizophrenia

Objective The Clock Drawing Test (CDT) is commonly used for cognitive screening, but there are few studies that compare performance on the CDT among schizophrenic patients of different ages. The objective of this study was to investigate the influence of schizophrenia and aging on performance in the CDT. Method Schizophrenic patients (N = 244) and a comparison group (N = 875) were recruited as subjects. Freedman's CDT was completed by all subjects, and the influences of disease and aging on performance in the CDT were examined. Multiple comparisons of the CDT scores between patients and the comparison group and within three age subgroups (young: less than 40 years, middle aged: 40–59 years, elderly: more than 60 years) were performed. Results There was a significant interaction of diagnosis and age, and the education significantly influenced the total score for all CDT conditions. For almost all age subgroups of patients, individuals with schizophrenia had significantly lower scores on all the CDT conditions than did the comparison group subjects. For patients and the comparison group, the elderly subgroup performed significantly worse than the young and middle-aged subgroups on almost all conditions of the CDT. Qualitative analysis of the clocks drawn revealed that the number of CDT categories in which schizophrenic patients scored significantly lower than the comparison group tended to increase with aging across both groups. Conclusions This study suggests that performance on the CDT was impaired not only by disease but also by aging. The study confirms that the CDT is sensitive enough to screen for cognitive impairments in schizophrenia.