It can take several months of sessions, and perhaps several stops and starts, to begin to develop a trusting relationship that can meaningfully address a clients issues. Epidemiology
The prevalence of personality disorder in the general community was largely unknown until surveys starting from the 1990s. In 2008 the median rate of diagnosable PD 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 cocaine, is described as a major public health concern requiring attention by researchers and clinicians.The prevalence of individual personality disorders ranges from about 2% to 8% for the more common varieties, such as obsessive-compulsive, 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 personality disorders. 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 personality disorders in total. Functional disability associated with the diagnoses appeared to be largely due to co-occurring mental disorders (Axis I in the DSM).
Enduring personality changes, not attributable to brain damage and disease (this is for conditions that seem to arise in adults without a diagnosis of personality disorder, following catastrophic or prolonged stress or other psychiatric illness). Other personality types and Millons description
Some types of personality disorder were in previous versions of the diagnostic manuals but have been deleted. Examples include sadistic personality disorder (pervasive pattern of cruel, demeaning, and aggressive behavior) and self-defeating personality disorder or masochistic personality disorder (characterized by behavior consequently undermining the persons pleasure and goals). They were listed in the DSM-III-R appendix as "Proposed diagnostic categories needing further study" without specific criteria. Psychologist Theodore Millon, a researcher on personality disorders, and other researchers consider some relegated diagnoses to be equally valid disorders, and may also propose other personality disorders or subtypes, including mixtures of aspects of different categories of the officially accepted diagnoses. Millon proposed the following description of personality disorders:

Additional factors
In addition to classifying by category and cluster, it is possible to classify personality disorders using additional factors such as severity, impact on social functioning, and attribution. Severity
This involves both the notion of personality difficulty as a measure of subthreshold scores for personality disorder using standard interviews and the evidence that those with the most severe personality disorders demonstrate a “ripple effect” of personality disturbance across the whole range of mental disorders.