Misclassification of dementia by the mini-mental state examination--are education and social class the only factors?

The 1988 Melton Mowbray Study of the Elderly comprised an initial screen with the Mini-Mental State Examination (MMSE) followed by a detailed clinical assessment using the Cambridge Mental Disorders of the Elderly Examination (CAMDEX) for all those scoring 21 and under on the MMSE, a one in two sample of those scoring 22 or 23 and a one in ten of the remainder. A total of 1579 subjects completed the initial screen with 438 subjects undergoing the CAMDEX assessment. Analysis of those subjects who were found to be free of dementia at the clinical assessment (n = 155) demonstrated that the very elderly, those from the manual social classes and subjects with visual impairments had an increased chance of being misclassified as demented by the MMSE. Low educational level and various measures of physical disability also showed a tendency to result in misclassification as falsely positive by the MMSE when viewed alone but these effects appeared to be due solely to their association with extreme age and/or manual social class.