Answer to Question 1
Community-based samples of adults have yielded lifetime prevalence rates of having at least one personality disorder at about 10 percent. The highest prevalence rates are for antisocial, obsessive-compulsive, and avoidant personality disorders. Narcissistic personality disorder seems to be the least common. Borderline personality disorder seems to be the most common in both inpatient and outpatient settings.
Answer to Question 2
Use of discrete categories leaves no way of describing people with traits who don't meet the criteria for a disorder. Because of common overlap in personality disorders, the final diagnosis (either using one diagnosis or two) doesn't provide an accurate description of individual traits. The dimensional approach is more complete, especially for individuals on the boundary of two disorders. The dimensional approach retains six of the 10 specific types of PD from the categorical system, which retains some continuity with the categorical system while allowing ratings of traits to replace the currently used diagnostic criteria.
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