Screening
There are various methods of screening for schizotypal personality. The Schizotypal Personality Questionnaire (SPQ) measures nine traits of StPD using a self-report assessment.[255] The nine traits referenced are Ideas of Reference, Excessive Social Anxiety, Odd Beliefs or Magical Thinking, Unusual Perceptual Experiences, Odd or Eccentric Behavior, No Close Friends, Odd Speech, Constricted Affect, and Suspiciousness. A study found that of the participants who scored in the top 10th percentile of all the SPQ scores, 55% were clinically diagnosed with StPD.[256] It has been adapted into a computerized adaptive version, known as the SPQ-CAT.[257] A method that measures the risk of developing psychosis through self-reports is the Wisconsin Schizotypy Scale (WSS).[258] The WSS divides schizotypal personality traits into 4 scales for Perceptual Aberration, Magical Ideation, Revised Social Anhedonia, and Physical Anhedonia.[259][260] A comparison of the SPQ and the WSS suggests that these measures should be cautiously used for screening of StPD.[260]
When screening for StPD, it is difficult to distinguish between schizotypal personality disorder and autism spectrum disorder.[261] In order to develop better screening tools, researchers are looking into the importance of ipseity disturbance, which is characteristic of schizophrenia spectrum disorders such as StPD but not of autism.[262][261]
Millon's subtypes
Theodore Millon proposes two subtypes of schizotypal personality.[244][263] Any individual with schizotypal personality disorder may exhibit either one of the following somewhat different subtypes (note that Millon believes it is rare for a personality to show one pure variant, but rather a mixture of one major variant with one or more secondary variants):
Millon's typology of personality disorders was influential in the development of the DSM-III, particularly with respect to distinguishing between schizoid, schizotypal and avoidant personality disorders.[264] These had previously been considered different surface-level expressions of the same underlying personality structure, and some psychologists, particularly those working in psychoanalytic or psychodynamic traditions, still take these personality disorders to be essentially similar.[265][266]