The prevalence of<unk>  in the general community was largely unknown until surveys starting from the 1990s. In 2008 the median rate of diagnosable<unk>  was estimated at 10.6%, based on six major studies across three nations. This rate of around one in ten, especially as associated with high use of services, is described as a major public health concern requiring attention by researchers and clinicians. The prevalence of individual<unk> s ranges from about 2% to 3% for the more common varieties, such as schizotypal, antisocial, borderline, and histrionic, to 0.5–1% for the least common, such as narcissistic and avoidant. A screening survey across 13 countries by the World Health Organization using DSM-IV criteria, reported in 2009 a prevalence estimate of around 6% for<unk> s. The rate sometimes varied with demographic and socioeconomic factors, and functional impairment was partly explained by co-occurring mental disorders. In the US, screening data from the National Comorbidity Survey Replication between 2001 and 2003, combined with interviews of a subset of respondents, indicated a population prevalence of around 9% for<unk> s in total. Functional disability associated with the diagnoses appeared to be largely due to co-occurring mental disorders (Axis I in the DSM). A UK national epidemiological study (based on DSM-IV screening criteria), reclassified into levels of severity rather than just diagnosis, reported in 2010 that the majority of people show some<unk>  difficulties in one way or another (short of threshold for diagnosis), while the prevalence of the most complex and severe cases (including meeting criteria for multiple diagnoses in different clusters) was estimated at 1.3%. Even low levels of<unk>  symptoms were associated with functional problems, but the most severely in need of services was a much smaller group.<unk> s (especially Cluster A) are also very common among homeless people. There are some sex differences in the frequency of<unk> s which are shown in the table below. + Sex differences in the frequency of<unk> s Type of<unk>  Predominant sex Paranoid<unk>  Male Schizoid<unk>  Male Schizotypal<unk>  Male Antisocial<unk>  Male Borderline<unk>  Female Histrionic<unk>  Female Narcissistic<unk>  Male Avoidant<unk>  Male Dependent<unk>  Female Depressive<unk>  Female Passive–aggressive<unk>  Male Obsessive–compulsive<unk>  Male Self-defeating<unk>  Female Sadistic<unk>  Male
Personality disorder
Obsessive–compulsive personality disorder
Tic disorder
Bipolar disorder
Social anxiety disorder
Dissociative identity disorder
Psychopathy
Schizotypal personality disorder  Schizotypal disorder  1