April 3, 2021
Morten Frisch is the lead author of a 2013 letter by European doctors criticizing the AAP task force on circumcision.  Two years after the letter was published, Frisch led a study based on his hypothesis that infant circumcision leads to a greater risk of boys developing autism spectrum disorder (ASP). Unsurprisingly Frisch concluded that the study of more than 340,000 boys in Denmark confirmed his expectation. 
Anthropologist Ava Neyer reviewed the study when it was first published and found several problems.  First, Frisch equated displaying a painful reaction with experiencing a pain reaction. Neyer expressed skepticism and observed, "Even if autistic children do have a higher perception of pain compared to neurotypical children in the same circumstance, it is quite a stretch to say that ‘lifelong deficits in stress response’ show that early pain causes autism. Is it that children with autism have deficits in their stress response or is it that children with autism find the world more inherently stressful due to other mechanisms?”
Frisch cited a study that reported that each 10% increase in a country’s circumcision rate was associated with a 0.2% increase in autism prevalence among boys. But Neyer found that that study was “examining a possible link between [Tylenol] usage and autism, not circumcision itself.” The study provided no information on the possible use of anesthetics during ritual circumcisions. 
Frisch admitted that the study did not include Jewish ritual circumcisions performed by mohels, nor procedures performed by non-Danish physicians. Certain data, such as ritual circumcisions performed in private clinics, were only available during a portion of the study period.
Frisch reported significant cultural differences between the uncircumcised Danish boys and circumcised Muslim boys that could factor into the differing autism rates. Furthermore, he compared the age of diagnosis in the United Kingdom with the age of diagnosis in Israel. Neyer noted that “children in Israel also undergo more thorough assessments for autism, which is possibly catching classic autism earlier. Cultural studies of autism reveal that diagnosis rates [among countries] change based on how countries view autism.”
Researcher bias and conflict of interest Under a section titled "Competing Interests", Frisch disclosed that he "has been an author of articles on health-related and sexual consequences of male circumcision and has taken part in national and international debates on the ethics of male and female circumcision.” Neyer researched Frisch online and quickly discovered "that he is an anti-circumcision activist with claims such as male circumcision leads to a bad sex life."
Neyer stated that she has no biases against the study, as she is personally opposed to RIC (routine infant circumcision), and she did not circumcise her sons. She explained, "I try to be more critical of studies that match what I wish to be true because I know I am naturally more inclined to believe ones that match my opinions, which is known as confirmation bias."
When analyzing studies, we routinely caution that while researcher bias doesn’t automatically discredit a study, readers should be particularly skeptical when considering a paper in which data, analysis, and conclusions support the researchers’ partisan agenda. In this case, Morten Frisch deliberately concealed his anti-circumcision agenda, including a lengthy history of advocacy against the procedure. One wonders whether he failed to be completely transparent because he's afraid that if readers were aware of his clear bias, they would treat the study with the appropriate skepticism that it deserves.
Morten Frisch admitted that “no firm conclusions should be drawn at this point", and he cautioned that his “findings obviously do not prove the suggested associations” between circumcision and autism." The U.S. Centers for Disease Control reviewed Frisch's study and rejected his conclusions. The CDC noted, "that study has been critiqued for methodological and analytic concerns, making the findings suspect."  Ava Neyer concluded that “one study is not enough to state that circumcision can double the risk of autism, especially a flawed study like this.”
For more discussion on confirmation bias, see our articles
 Morten Frisch et al; "Cultural Bias in the AAP’s 2012 Technical Report and Policy Statement on Male Circumcision"; Pediatrics; April 2013. The AAP Task Force responded to Frisch's criticism. Susan Blank et al; "Cultural Bias and Circumcision: The AAP Task Force on Circumcision Responds"; Pediatrics; April 2013.
 Morten Frisch and Jacob Simonsen; “Ritual circumcision and risk of autism spectrum disorder in 0- to 9-year-old boys: national cohort study in Denmark”; Journal of the Royal Society of Medicine; January 8, 2015
 Ava Neyer, “The problem with articles on autism risks and how to evaluate studies. Or why circumcision is unlikely to increase rates of autism”; The Chimerical Capuchin; January 10, 2015
 Ann Z Bauer and David Kriebel, “Prenatal and perinatal analgesic exposure and autism: an ecological link”; Environmental Health; May 9, 2013
 "Summary of Public Comments and CDC Responses to Public Comments for Information for Providers to Share with Male Patients and Parents Regarding Male Circumcision and the Prevention of HIV infection, Sexually Transmitted Infections, and other Health Outcomes"; U.S. Centers for Disease Control and Prevention; August, 2018