Epidemiology of dementia - with particular focus on time trends and methodology

Abstract: Dementia is a clinical syndrome characterised by deterioration in cognitive functions, which causes personal suffering and societal challenges. Studies investigating the incidence, prevalence, and mortality of dementia are needed for the understanding of the societal and economic burden of the disease. Epidemiological studies of dementia face methodological challenges. This thesis examined the time trends in dementia epidemiology among octogenarians, an age group rapidly increasing and where dementia is common. Methodological considerations, such as selection bias and the impact of the choice of diagnostic tools, were also studied. Data used in the papers was derived from the population-based Gothenburg H70 Birth Cohort Studies, and the Prospective Population Study of Women in Gothenburg, Sweden. The cohorts included were born in 1901-02, 1923-24, and 1930. Findings from Paper I showed that participants in general, had a lower prevalence of disorders, higher educational level, and were more often married than refusals. There were fewer differences in comparison with the target population of same-aged individuals in Gothenburg. In Paper II, we found that the diagnostic criteria in ICD-10 yielded the lowest prevalence of dementia and ICD-11 the highest, followed by the DSM-5. The agreement between the DSM-5 and ICD-11 was substantial. In Paper III, we found that the survival time increased both in those with and without dementia. Dementia was the most important predictor of death in both cohorts. Lastly, in Paper IV, we found a decreased prevalence of dementia at ages 85 and 88. We also found a decrease in the four-year incidence of dementia. The findings from this thesis provide insights into the time trends in the epidemiology of dementia, as well as into important aspects of methodological considerations in dementia research.