▁to ▁decre ases ▁in ▁the ▁age ▁of ▁diagn osis . ▁ ▁A ▁ 2 0 0 9 ▁study ▁of ▁California ▁data ▁found ▁that ▁the ▁reported ▁inc idence ▁of ▁aut ism ▁rose ▁ 7 - ▁to ▁ 8 - fold ▁from ▁the ▁early ▁ 1 9 9 0 s ▁to ▁ 2 0 0 7 , ▁and ▁that ▁changes ▁in ▁di agnostic ▁criteria , ▁inclusion ▁of ▁mil der ▁cases , ▁and ▁earlier ▁age ▁of ▁diagn osis ▁probably ▁explain ▁only ▁a ▁ 4 . 2 5 - fold ▁increase ; ▁the ▁study ▁did ▁not ▁quant ify ▁the ▁effects ▁of ▁wider ▁aw aren ess ▁of ▁aut ism , ▁increased ▁fund ing , ▁and ▁expand ing ▁treatment ▁options ▁resulting ▁in ▁parents ' ▁greater ▁motiv ation ▁to ▁seek ▁services . ▁Another ▁ 2 0 0 9 ▁California ▁study ▁found ▁that ▁the ▁reported ▁increases ▁are ▁unlikely ▁to ▁be ▁explained ▁by ▁changes ▁in ▁how ▁qual ifying ▁condition ▁codes ▁for ▁aut ism ▁were ▁recorded . ▁ ▁Several ▁environmental ▁risk ▁factors ▁have ▁been ▁proposed ▁to ▁support ▁the ▁hypothesis ▁that ▁the ▁actual ▁frequency ▁of ▁aut ism ▁has ▁increased . ▁These ▁include ▁certain ▁food s , ▁inf ect ious ▁disease , ▁p estic ides . ▁There ▁is ▁over wh el ming ▁scientific ▁evidence ▁against ▁the ▁M MR ▁hypothesis ▁and ▁no ▁convin cing ▁evidence ▁for ▁the ▁th iom ers al ▁( or ▁Th imer os al ) ▁hypothesis , ▁so ▁these ▁types ▁of ▁risk ▁factors ▁have ▁to ▁be ▁ruled ▁out . ▁Although ▁it ▁is ▁unknown ▁whether ▁aut ism ' s ▁frequency ▁has ▁increased , ▁any