disorders like schizophrenia, bipolar disorder, and ADHD. Gut microbiome has a relation to ASD. Excessive Clostridia spp. was found in children with ASD and gastrointestinal difficulties; Clostridia spp produces propionic acid, which is impaired or in excess in people with ASD. Specifically, C. tetani and C. histolyticum are two species of this bacteria that affect people with ASD. C. tetani produces tetanus neurotoxin in the intestinal tract; C. histolyticum is a toxin producer that is abundant in people diagnosed with ASD. Both of these could contribute to neurological symptoms. There is also controversy over the Nature vs. Nurture debate. According to family studies, genetic and environmental factors have an equal influence on risk of ASD. Vaccines A later-retracted article from The Lancet making false claims provoked concern about vaccines among parents. Its author was found to be on the payroll of litigants against vaccine manufacturers. The idea of a link between vaccines and autism was extensively investigated and shown to be false. The scientific consensus is that there is no relationship, causal or otherwise, between vaccines and incidence of autism, and vaccine ingredients do not cause autism. Nevertheless, the anti-vaccination movement continues to promote myths, conspiracy theories and misinformation linking the two. A developing tactic appears to be the "promotion of irrelevant research [as] an active aggregation of several questionable or peripherally related research studies in an attempt to justify the science underlying a questionable claim." Intelligence The percentage of autistic individuals who also meet criteria for intellectual disability has been reported as anywhere from 25% to 70%, a wide variation illustrating the difficulty of assessing autistic intelligence. For pervasive developmental disorder not otherwise specified (PDD-NOS), the association with intellectual disability is much weaker. The diagnosis of Asperger syndrome excludes clinically significant delays in mental or cognitive skills. A 2007 study suggested that Raven's Progressive Matrices (RPM), a test of abstract reasoning, may be a better indicator of intelligence for autistic children than the more commonly used Wechsler Intelligence Scale for Children (WISC). Researchers suspected that the WISC relied too heavily on language to be an accurate measure of intelligence for autistic individuals. Their study revealed that the neurotypical children scored similarly on both tests, but the autistic children fared far better on the RPM than on the WISC. The RPM measures abstract, general and fluid reasoning, an ability autistic individuals have been presumed to lack. A 2008 study found