Manfield adds "This huge discrepancy [from the ten percent reported by therapists for the condition] is probably largely because someone with a schizoid disorder is less likely to seek treatment than someone with other axis-II disorders. "A 2008 study assessing personality and mood disorder prevalence among homeless people at New York City drop-in centres reported an SzPD rate of 65% among this sample. The study did not assess homeless people who did not show up at drop-in centres, and the rates of most other personality and mood disorders within the drop-in centres was lower than that of SzPD. The authors noted the limitations of the study, including the higher male-to-female ratio in the sample and the absence of subjects outside the support system or receiving other support (e.g., shelters) as well as the absence of subjects in geographical settings outside New York City, a large city often considered a magnet for disenfranchised people.A University of Colorado Colorado Springs study comparing personality disorders and Myers–Briggs Type Indicator types found that the disorder had a significant correlation with the Introverted (I) and Thinking (T) preferences. History
The term "schizoid" was coined in 1908 by Eugen Bleuler to designate a human tendency to direct attention toward ones inner life and away from the external world, a concept akin to introversion in that it was not viewed in terms of psychopathology. Bleuler labeled the exaggeration of this tendency the "schizoid personality".
This profile is summarized in the table reproduced below that lists clinical features that involve six areas of psychosocial functioning and are organized by "overt" and "covert" manifestations. "Overt" and "covert" are intended to denote seemingly contradictory aspects that may both simultaneously be present in an individual. These designations do not necessarily imply their conscious or unconscious existence. The covert characteristics are by definition difficult to discern and not immediately apparent. Additionally, the lack of data on the frequency of many of the features makes their relative diagnostic weight difficult to distinguish at this time. However, Akhtar states that his profile has several advantages over the DSM in terms of maintaining historical continuity of the use of the word schizoid, valuing depth and complexity over descriptive oversimplification and helping provide a more meaningful differential diagnosis of SzPD from other personality disorders. Causes
Some evidence suggests the cluster A personality disorders have shared genetic and environmental risk factors, and there is an increased prevalence of SzPD in relatives of people with schizophrenia and schizotypal personality disorder. Twin studies with SzPD traits (e.g. low sociability and low warmth) suggest these are inherited. Besides this indirect evidence, the direct heritability estimates of SzPD range from 50 to 59%. To Sula Wolff, who did extensive research and clinical work with children and teenagers with schizoid symptoms, "schizoid personality has a constitutional, probably genetic, basis."