To investigate and make valid estimates of the occurrence of dementia and the most common subtypes of dementia in Trøndelag, and transfer these figures to estimates of the occurrence of dementia in Norway as a whole, by age, sex and severity of dementia. Furthermore, the proportion of people without dementia diagnosis among those with dementia will be examined. The investigators will further investigate whether there are differences in dementia prevalence between males and females and educational groups and look at factors associated with a lack of diagnosis.

Introduction There are currently no valid estimates of the occurrence of dementia in Norway. Estimates in use range from 70.000 to 104.000, with the highest estimate being 50 percent greater than the lowest. This makes it difficult to plan today's health services and estimate future needs.

To enable good planning of services to people with dementia, it is important that people with dementia to be evaluated and diagnosed for their illness. An early diagnosis seems to improve prognosis for the course of the disease. The proportion of undiagnosed people with dementia differs in the studies done on this and it is unclear which factors that may explain why many remain undiagnosed for their dementia disease. As a quality measure on the cognitive data being collected in this study we will make population-based Norwegian norms for the Montreal Cognitive Assessment Test (MoCA) test and the Ten-word delayed recall test from CERAD.

The aim of this study is to provide knowledge that is crucial for planning good health and care services for older people with cognitive impairment and dementia. We will make valid estimates for the prevalence of dementia and the most common subtypes of them in Trøndelag and transfer these figures to estimates to Norway as a whole, by age, gender and severity of disease. We will investigate whether there are differences in dementia prevalence between males and females and educational groups. Furthermore, there will be made a survey of the proportion of people without dementia diagnosis among those with dementia, and examine the factors associated with a lack of diagnosis.

Method The data collection was a collaboration with the Health Survey in Nord-Trøndelag when this was carried out for the fourth time (HUNT4) in the period 2017-2019. All persons over the age of 70 living in 23 municipalities in Nord-Trøndelag and a district in Trondheim municipality (Trøndelag) were invited to an assessment at a field stations or by home visits (including institutionalized care), in the study parts called HUNT4 70+ and HUNT4 Trondheim 70+. The participants were offered a survey of cognition and function in everyday life. To get more information on cognitive function an interview with next of kin were made for participants with possible cognitive impairment.

A diagnostic work-up group of scientific and clinical experts (geriatrics, old age psychiatry or neurology) assessed the cases and made the research-based diagnosis. Standard diagnostic criteria according to the DSM-5 was applied for all the dementia diseases. The new estimates from Trøndelag will be used to estimate the occurrence of dementia in Norway as a whole, by age, sex and severity of dementia. Furthermore, the proportion of people without dementia diagnosis among those with dementia will be examined. Information about known dementia diagnosis from dementia assessment in municipality or specialist health service will be obtained by linking to registered data. The investigators will further investigate whether there are differences in dementia prevalence between males and females and educational groups and look at factors associated with a lack of diagnosis. Information from the earlier waves of HUNT (1-4) will be used to get information on health and risk factors for dementia from the study population.

Inclusion Criteria:

• Living in the designated area

Exclusion Criteria:

• None

Persons of 70 years of age or older participated in HUNT4 and accepted cognitive screening in HUNT4 70+.