Anti-social conduct
Another study looked at rates of anti-social conduct in boys with either SzPD or Asperger syndrome compared with a control group of non-schizoid individuals and found the incidence of anti-social conduct to be the same in both groups. However, the schizoid boys stole significantly less. Upon follow-up in adulthood, out of a matched group of 19 boys with SzPD and 19 boys without, four of the schizoid boys reported having exclusively internal violent fantasies (concerned with Zulu wars, abattoirs, fascists and communists and a collection of knives, respectively), which were pursued entirely by themselves, while the only non-schizoid subject to report a violent fantasy life shared his with a group of young men (dressing up and riding motorcycles as a self-styled "panzer" group).An absent parent or socio-economic disadvantage did not seem to affect the risk of anti-social conduct in schizoid individuals as much as it did in non-schizoid individuals. Absent parents and parental socio-economic disadvantage were also less common in the schizoid group. Controversy
The original concept of the schizoid character developed by Ernst Kretschmer in the 1920s comprised an amalgamation of avoidant, schizotypal and schizoid traits. It was not until 1980 and the work of Theodore Millon that led to splitting this concept into three personality disorders (now schizoid, schizotypal and avoidant). This caused debate about whether this was accurate or if these traits were different expressions of a single personality disorder.
A 2011 study on suicidal inpatients at a Moscow hospital found that schizoids were the least common patients, while those with cluster B personality disorders were the most common. Asperger syndrome
Several studies have reported an overlap or comorbidity with the autism spectrum disorder Asperger syndrome. Asperger syndrome had traditionally been called "schizoid disorder of childhood", and Eugen Bleuler coined both the terms "autism" and "schizoid" to describe withdrawal to an internal fantasy, against which any influence from outside becomes an intolerable disturbance. In a 2012 study of a sample of 54 young adults with Asperger syndrome, it was found that 26% of them also met criteria for SzPD, the highest comorbidity out of any personality disorder in the sample (the other comorbidities were 19% for obsessive–compulsive personality disorder, 13% for avoidant personality disorder and one female with schizotypal personality disorder). Additionally, twice as many men with Asperger syndrome met criteria for SzPD than women. While 41% of the whole sample were unemployed with no occupation, this rose to 62% for the Aspergers and SzPD comorbid group. Tantam suggested that Asperger syndrome may confer an increased risk of developing SzPD. A 2019 study found that 54% of a group of males aged 11 to 25 with Asperger syndrome showed significant SzPD traits, with 6% meeting full diagnostic criteria for SzPD, compared to 0% of a control.In the 2012 study, it was noted that the DSM may complicate diagnosis by requiring the exclusion of a pervasive developmental disorder (PDD) before establishing a diagnosis of SzPD.