INTRODUCTION

The process of identifying risk factors for dementia is a long one, that typically begins with an astute clinician who observes that a given factor or agent seems to be associated with a specific disorder. These initial observations often are followed by case-control studies, in which patients with the disease of interest are compared with healthy control subjects to determine whether or not the suspected risk factors are more frequent among those with the disease than those without. While clinical observations and case-control studies provide important clues about potential risk factors, limitations inherent in these methods (e.g. selection bias) restrict conclusions about risk factors that can be drawn from them. Large-scale, population- or community-based epidemiological investigations can control for some of the limitations associated with clinical research and can more definitively assess potential risk factors.

In recent years, there have been a number of community-based epidemiological studies of dementia and associated risk factors. In this chapter, we review studies of the incidence and prevalence of dementia associated with various disorders. Prevalence represents the total number of cases of a disease in a defined population at a given time; incidence represents the number of people in a defined population who develop a disease in a given time period. The prevalence of a disease in a population is the function of both the incidence rate and the duration of the disease.