First Lifetime Prevalence

According to Public Mental Health (Eaton et al., 2012), one of the first challenges to increasing our understanding of mental health in the general population is determining how to define the health-related burden and etiology of mental disorders. Determining incidence and prevalence are equally important in the assessment of mental disorders, but each provides distinct, unique information.
Prevalence provides essential summary information that is important when determining the burden of mental disorders (Eaton et al, 2012). There were three types of prevalence estimates discussed during this course to describe mental disorders: lifetime, point, and period prevalence. Lifetime prevalence refers to the proportion of people who currently have or have ever had a condition, while point prevalence describes the
proportion of people who have a given condition at a given time (e.g. now). Meanwhile, period prevalence refers to the proportion of people who have a condition during a stated period of time (e.g. 12 months). Period and point prevalence are most useful for assessing mental health needs (e.g. services, resources) at a given time, while lifetime prevalence is especially useful for assessing the proportion of the population surviving a given mental disorder (Pederson et al., 2014).
On the other hand, incidence, defined as the rate that new cases of a disease occur, is of particular meaning when assessing risk factors prospectively (Eaton et al, 2012).
More specifically, incidence is a key component to assessing the etiology and course of mental disorders, or the “force of morbidity” of mental disorders (Pederson et al., 2014). These factors are also important in planning mental health services. In psychiatric epidemiology, at-risk persons included in incidence estimates are defined as those with “no history of the mental disorder over their lifetime up to and including the present” (Eaton et al, 2012). Therefore, incidence is best referred to as “first lifetime incidence”. For this course, cumulative and annual were also described. Cumulative incidence refers to the frequency of a disorder over a period of time, while the annual incidence describes the frequency of a given disorder over the course of a year. The annual incidence is especially useful for assessing changes in the etiology of mental disorders, while cumulative incidence is particularly useful for determining the lifetime risk for mental disorders (Pederson et al,
2014).
Taken together, prevalence and incidence are both key components of the descriptive and analytic epidemiology of mental disorders. While they both have their own set of measurement challenges, data collected during the 3rd generation of psychiatric epidemiologic research has made it possible to use these methods to enrich our understanding of the burden, course, and etiology of mental disorders.