Introduction
tbegun to be scientifically investigated. This development has taken place because a number of standardized instruments to assess personality and PD in an empirical fashion have been developed, in parallel with the refinement of a valid and reliable diagnostic system based on a categorical approach. The need for the epidemiological investigation of PDs seems justified for several reasons.
1 As seen in recent epidemiological surveys, PDs are frequent and have been found in different countries and sociocultural settings.
2 PDs can seriously impair the life of the affected individual and can be highly disruptive to societies, communities, and families.
3 Personality status is often a major predictive variable in determining the outcome of Axis I mental disorders and the response to treatment.
In this chapter, we review the epidemiological literature on PDs up to October 2007, focusing on studies carried out since the development of the DSM-III. First, community prevalence studies of PDs are reviewed. We then look at the prevalence of individual PDs in the community. Finally, we consider the prevalence of PDs in clinical populations, and in special settings (e.g. primary care, prisons, etc.).
Community epidemiological studies of unspecified personality disorders
Until the development of the DSM-III diagnostic criteria for PDs and the subsequent availability of standardized assessment instruments, epidemiological studies aimed at assessing the prevalence rate of PDs were hampered by severe methodological limitations, including differences in sampling methods and in diagnostic criteria, the known unreliability of PD diagnoses based on clinical judgement, and the lack of standardized assessment methods. Since 1980, twelve main studies with at least 200 subjects sampled have ascertained the prevalence rate of PDs in different community samples using assessment instruments specific for PD; they are shown in
Table 4.12.4.1.
In these studies, the sample sizes ranged between 200 and 2053 subjects, with an average sample of 565.4; all surveyed individuals were evaluated by means of a specific PD assessment instrument, mainly a structured interview. While most studies were carried out in one stage, Lenzenweger
et al.
(6) first screened a large sample of university students with a self-administered Axis II inventory, and then interviewed a subgroup of 258 subjects using the International Personality Disorder Examination. The median prevalence rate of any PDs in these eight studies is 12.5 per cent.
Two large community studies
(13,14) carried out in the USA were not included in
Table 4.12.4.1 since PD prevalence rates were based
on screening questions
(13) and on a newly developed fully diagnostic structured interview carried out by lay interviewers rather than clinicians, which lacked any accompanying validity data.
(14)In the surveys considered here, the rate of PDs decreases in older age groups; although the sex ratio is different for specific types of PD (e.g. more schizoid, narcissistic, and antisocial PDs among males, more dependent, avoidant, and histrionic PDs among females), the overall rates of PD are about equal for both sexes. Finally, prevalence rates are generally higher in urban populations and lower socio-economic groups.
