Because this extremely small study (666 children total) relies upon self-report and the differences in groups it considers only includes health problems that are easily denied, the results are completely flawed. Many people who do not believe in vaccinations would never take their child to a pediatrician to by diagnosed with subjective health problems such as ADHD, autism, allergies, learning disabilities, etc. Therefore, the unvaccinated group was less likely to be diagnosed with these problems, even if they suffered from them at the same rate as the vaccinated group. When the two groups (vaccinated and not vaccinated) are compared in much larger studies, across the entire nation of the USA, eliminating parental determination of morbidity, the only differences between groups that are found are that unvaccinated children are far more likely to develop vaccine-preventable potentially fatal illnesses . Here are the real facts: https://www.cdc.gov/vaccines/parents/diseases/child/pertussis.html