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All nine persons aged 100 or older in a Dutch town with some 100,000 inhabitants were examined by means of cognitive tests, informant questionnaires, and clinical interviews. Formal testing was difficult in most subjects because of visual, auditory, and motor handicaps. By combining the results of cognitive tests and clinical examinations, a diagnosis of moderate to severe dementia could be made in eight subjects. One subject was not examined but by informant questionnaire was found to be mildly demented.
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Thomassen et al. (1998) studied this question.
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