of autistic children, using parents of children with Down syndrome as controls. Using standardized tests it was found that parents of autistic children were "more aloof, untactful and unresponsive" compared to parents whose children did not have autism. A 1997 study found higher rates of social and communication deficits and stereotyped behaviors in families with multiple-incidence autism. Autism was found to occur more often in families of physicists, engineers and scientists. 12.5% of the fathers and 21.2% of the grandfathers (both paternal and maternal) of children with autism were engineers, compared to 5% of the fathers and 2.5% of the grandfathers of children with other syndromes. Other studies have yielded similar results. Findings of this nature have led to the coinage of the term "geek syndrome". A 2001 study of brothers and parents of autistic boys looked into the phenotype in terms of one current cognitive theory of autism. The study raised the possibility that the broader autism phenotype may include a "cognitive style" (weak central coherence) that can confer information-processing advantages. A study in 2005 showed a positive correlation between repetitive behaviors in autistic individuals and obsessive-compulsive behaviors in parents. Another 2005 study focused on sub-threshold autistic traits in the general population. It found that correlation for social impairment or competence between parents and their children and between spouses is about 0.4. A 2005 report examined the family psychiatric history of 58 subjects with Asperger syndrome (AS) diagnosed according to DSM-IV criteria. Three (5%) had first-degree relatives with AS. Nine (19%) had a family history of schizophrenia. Thirty five (60%) had a family history of depression. Out of 64 siblings, 4 (6.25%) were diagnosed with AS. According to a 2022 study held on 86 mother-child dyads across 18 months, "prior maternal depression didn’t predict child behavior problems later." Twinning risk It has been suggested that the twinning process itself is a risk factor in the development of autism, presumably due to perinatal factors. However, three large-scale epidemiological studies have refuted this idea. These studies took place in California, Sweden, and Australia. One study done in Western Australia, utilized the Maternal and Child Health Research Database that houses birth records for all infants born, including infants and later children diagnosed with autism spectrum disorder. During this study, the population analyzed for the incidence of Autism Spectrum Disorder was restricted to those children with birth years between 1980 and 1995. The