Dementia and mild cognitive impairment in older people in Trøndelag.

BACKGROUND:The number of people with dementia is expected to triple by 2050. We present figures showing the prevalence of dementia and mild cognitive impairment in Trondheim, and show how weighting for non-response and nursing home residency affects these figures when comparing Trondheim with Nord-Trøndelag. MATERIAL AND METHOD:In the fourth data collection in the Trøndelag Health Study (HUNT4) in the Norwegian county of Trøndelag, people aged 70 and over in Trondheim were invited to participate in HUNT4 Trondheim 70+. The participants were interviewed and underwent cognitive testing. A diagnostic team diagnosed dementia and mild cognitive impairment. Weights adjusting for non-response bias were used in the comparison of Trondheim and Nord-Trøndelag. RESULTS:The prevalence of dementia in Trondheim was estimated at 16.2 % for the age group 70 years and over, after weighting for non-response bias with regard to age, sex, education and proportion of nursing home residents. Unadjusted dementia prevalence was 21.0 % in Trondheim and 15.7 % in Nord-Trøndelag. After weighting, the prevalence was almost identical in the two samples. INTERPRETATION:Weighting for non-response is crucial for obtaining representative figures in prevalence studies of dementia.