Prevalence of dementia in an urban slum population in thailand: Validity of screening methods

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Abstract
A randomly selected sample of 500 subjects over 60 years old and their relatives were studied using standardized methods for assessment of cognitive impairment. The prevalence of DSM‐III‐R dementia was 1.8% (95% confidence intervals 0.6‐3%), and the majority of cases had a probable diagnosis of Alzheimer's disease. The sensitivity and specificity of the field survey version of the Mini‐Mental State Examination (MMSE) for a diagnosis of dementia using a threshold of 21 were 100% and 53% respectively. This was associated with a positive predictive value of dementia, given a low score, of only 3%. A high prevalence of low MMSE scores was found: 23% of men and 50% of women had scores below 21, and there were strong relationship between low scores and age. Strong associations between low MMSE scores and no education were found, and weaker associations with female sex, deafness and poor sight. The MMSE is markedly affected by educational level, which together with its low positive predictive value for dementia in this population makes it a poor screening of research tool. A Behaviour Rating Scale score had a higher specificity leading to fewer false positives, but only achieved a sensitivity of 67%. In populations with low levels of education it is recommended that behavioural disabilities scales should be developed as a means of screening for dementia syndromes.