>>reporter: doctor john schwartzberg uc berkeley says researchers says the people of autistic childrennetics may predispose them to autism. >> this might be a group where if vaccines could cause autism it might show up more easily. and it didn't show up at all. >>reporter: anti- back to -- vaccine activists said it was flawed didn't look at potentially all disorders. psychologist say it's human nature to stick with beliefs. >> they believe this irrespective evidence and they will keep their attitude. >>reporter: there's also what's called omission bias parents heading towards doing nothing if they think there is a risk to their children. >> don't believe everything you think, think, right, of course we are going to gear on the side of our own biases. that's the problem. >>reporter: doctor say one disappointing thing about this study is that it took precious research dollars to prove again what science is already established. there is no link between vaccines and autism. and still some vaccine deniers cling to their beliefs john ktvu fox2 news. >>> sacrum -- sacramento now it allows par