ably ▁the ▁best , ▁screens ▁a ▁large ▁sample ▁of ▁an ▁entire ▁community ▁to ▁identify ▁possible ▁cases , ▁and ▁then ▁evalu ates ▁each ▁possible ▁case ▁in ▁more ▁detail ▁with ▁standard ▁di agnostic ▁procedures . ▁This ▁last ▁method ▁typically ▁produces ▁the ▁most ▁reliable , ▁and ▁the ▁highest , ▁pre val ence ▁estimates . ▁ ▁Fre quency ▁estimates ▁Est im ates ▁of ▁the ▁pre val ence ▁of ▁aut ism ▁vary ▁widely ▁depending ▁on ▁di agnostic ▁criteria , ▁age ▁of ▁children ▁screen ed , ▁and ▁ge ographical ▁location . ▁Most ▁recent ▁reviews ▁tend ▁to ▁estimate ▁a ▁pre val ence ▁of ▁ 1 – 2 ▁per ▁ 1 , 0 0 0 ▁for ▁aut ism ▁and ▁close ▁to ▁ 6 ▁per ▁ 1 , 0 0 0 ▁for ▁AS D ; ▁P DD - N OS ▁is ▁the ▁vast ▁majority ▁of ▁AS D , ▁As per ger ▁synd rome ▁is ▁about ▁ 0 . 3 ▁per ▁ 1 , 0 0 0 ▁and ▁the ▁at yp ical ▁forms ▁child hood ▁dis integr ative ▁dis order ▁and ▁R ett ▁synd rome ▁are ▁much ▁r ar er . ▁ ▁A ▁ 2 0 0 6 ▁study ▁of ▁nearly ▁ 5 7 , 0 0 0 ▁British ▁nine - ▁and ▁ten - year - olds ▁reported ▁a ▁pre val ence ▁of ▁ 3 . 8 9 ▁per ▁ 1 , 0 0 0 ▁for ▁aut ism ▁and ▁ 1 1 . 6 1 ▁per ▁ 1 , 0 0 0 ▁for ▁AS D ; ▁these ▁higher ▁figures ▁could ▁be ▁associated ▁with