Assessment of cognitive function

Cognitive function was assessed using MMSE [17], a brief, validated instrument commonly used to screen for dementia. MMSE scores range from 0 to 30, with lower scores indicating greater cognitive impairment. Cognitive impairment was defined as an MMSE score of <24 [18, 19]. Using this cutoff value, the area under the receiver operating characteristic curve of MMSE for dementia diagnosed based on the Diagnostic and Statistical Manual of Mental Disorders Third Edition Revised (DSM-III-R), a classification system for mental illnesses developed by the American Psychiatric Association, in a Japanese population has been reported to be as high as 0.980 [18].