In this chapter, we discuss the epidemiology and comorbidity of the personality disorders with special emphasis on later life. In the mental health field, epidemiology is defined as the study of the frequency and distribution of psychiatric disorders in a population. Epidemiological research is crucial to the understanding of rates of disorders as well as how they vary according to social, cultural, and individual factors (e.g., socioeconomic status, ethnicity, religion, gender, age). Psychiatric epidemiology typically focuses on the following primary variables:
■ Prevalence refers to the proportion of a population that has a disorder at any point in time. Prevalence data for most mental disorders are summarized in the text of the DSM-IV-TR.
■ Incidence refers to the number of new cases of a disorder that occur in a specific period (1 year is a common incidence cycle). Notably, incidence and prevalence are related: As incidence for any mental disorder increases (or decreases) over time, there will be a corresponding increase (or decrease) in the prevalence of the disorder, although this will be much more gradual.
■ Risk factors refer to conditions or variables that, if present, increase the likelihood of developing a disorder. For example, childhood adversity (e.g., sexual abuse, chaotic family environment) has been studied as a potential risk factor for a host of personality disorders.
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