# OAR Box 1126

Prepped by Ollie Stewart



### Document

Number: 

# 6)11-1-12 7 Docket Number: 

# A-83-2 2

Printed 4/18/2008 9:58:21 AM Sheet 6 of 182 P. 1P. 2

Clair e B . Ernhar t Octobe r 7 , 198 3
Respons e t o Appendi x12- C INDEPENDEN

T PEER-REVIE WO F SELECTE D STUDIE S CONCERNIN G NEUROBEHAVIORAL EFFECT S O F LEA D EXPOSURE S I NNOMINALL Y ASYMPTOMATI C CHILDREN ? OFFICIAL REPORT O F FINDING S AN D RECOMMENDATION S O F A NINTERDISCIPLINAR

Y EXPERT REVIE WCOMMITTE E I' d lik e firs t t o commen d th e Committe e fo r th e objectivit yo f it s analyse s an

d fo r th e car e wit hwhic hi t reviewe d th e material s provided . I concu r wit hmos t o f wha t i s include d i n th e repor t an d I onl ywis htha t I had mor e an d bette r dat a wit hwhic hI coul d answe r mor e definitivel yth e question s pose d b ythe Committee » O n onl yon e suggestion , discusse d below , woul d I disagre e wit hthe recommend

ations . Th e introductio n presente d wel l th e mor e critica l o f th e issue s relevan t t o th e design o f researc hi n thi s area . Th e weaknesse s o f cross - sectiona l design s ar e wel l stated . Wit hth e completio n o f the veryimportan t U.K . studies , w e wil l probabl yse e fewe r cross-sectiona l studies . Meanwhile , w e ar e waiting fo r th e result s an

d dealing wit hth e difficul t problem s arising i n th e conduc t o f th e prospectiv e studies . Th e balanc e o f thes e comment s deal s wit hthe revie wo f the studie s b

ym yassociate s an

d me . A t the time thi s revie wwa s written , the Committe e di d no t hav e m yrepor t o f furthe r analyse s o f m ydata . Whil e thes e wer e no t conducte d precisel ya s suggeste d b y th e Committe e i n th e repor t a t hand , th e majo r suggestion s wer e implemente d a s wel l a s possibl e an d I fee l tha t furthe r manipulatio n o f the dat a i s no t warranted . Specifi c Points : P.15 , firs t paragraph . Al l analyse s o f reading score s had ag e a t time o f testing entere d a s th e firs t covariate . Perhap s regres sing rawscore s fo r the McCarth yscale s o n ag e rathe r than using extrapolate d o r norme d score s woul d hav e bee n better . I' mconcerne d abou t the regressio n effect s inheren t i n tha t approach . I t seem s highl yunlikel ytha t thi s woul d influenc e th e result s i n an y appreciabl e way . P.15 , las t paragraph . I n th e reanalyse s provide d educatio n wa s force d int o the covariat e se t althoughi t wa s no t significantl y relate d t o the outcome measur e i n an yanalysi s afte r entr yo f paren t I.Q . I can se e th e merit s o f the backwar d selectio n procedur e i n thi s kin

d o f analysis . I n thi s case , I doub t tha t taking i t bac k ou t woul d hav e mad e an

ydifference .P. 3

P.1 7 (f) o I wa s unawar e tha t Perin o had mor e highlea d case s earl yi n th e dat a collectio n period . Hi s wif e se t u p the dat a collectio n schedule . Sinc e h e wa s blinde d an d wel l trained , I don' t think th e orde r ha d a n effect , bu t i t wa s no t ideal . P.18 . I had considere d handling th e dat a a s a cross-lagge d pane l design a s on e wayo f assessing th e possiblit ytha t earl y deficit s i n intelligenc e coul d lead t o highe r level s o f lead . A s noted , th e cros s correlation s wer e lowan d no t appreciabl ydifferen t fro meac hothe r s o I gav e u p tha t approacho I n some o f m ypresen t work , I' m

developing causa l model s t o handl e thes e problem s o f longitudina l relationships . I question , however , whethe r ther e i s muc hmor e tha t ca n b e don e i n tha t regar d wit hth e se t o f dat a unde r review . Th e problem s o f measuring chang e ar e ol d familia r concerns . A simpl e chang e scor e fo r th e intelligenc e measur e wa s adde d t o th e se t o f reanalyse s supplie d i n August . Residual s compute d fro mthe regressio n o f th e late r measur e o n th e earlier , a s suggeste d b yDr . Jones , woul d hav e give n a somewha t differen t resolutio n o f th e problem , bot hnumericall yan d i n th e sens e o f wha t th e mode l repre sents . Asid e fro

mal l th e problem s involve d i n th e measuremen t o f change , th e ide a o f chang e i n intelligenc e a s a outcome variabl e relate d t o th e earl yexposur e inde xi s reasonable . On e ca n als o pu t fort ha rational e fo r chang e i n lea d leve l a s an outcome measur e relate d t o earl yintelligence . (Les s intelligen t childre n ma

yb e mor e likel yt o b e expose d o r mor e intelligen t childre n t o sta

yawayfro

mit. ) I n bot ho f th e abov e design s th e concer n i s wit hth e effec t o f th e earlie r conditio n o n change . Wha t Dr . Jone s suggested , however , i s tha t bot hIste r measure s b e regresse d o n the corresponding earlie r measures ; thi s essentiall ycancel s eithe r a s a plausibl e etiologica l facto r i n th e :aodel . Th e residualizatio n o f th e lea d measur e i s o f particula r con : -ir

n bot hbecaus e th e mor e frequentl yhypothesize d directio n o f e; . fee t i s fro m lea d t o defici t an

d becaus e lea

d leve l droppe d appreciabl yfro mth e preschoo l t o the schoolag e time o f assessment . I f lea d level s i n th e rang e unde r consideratio n d o hav e a n effect , th e earlie r highe r level s ar e o f muc hgreate r concer n tha n the late r levels . Thi s i s particularl ys o i f ther e i s an y possibilit yo f a threshol d o f effec t withi n thi s range . Th e availabilit yo f th e earl ylea d measur e i s wha t make s thi s a longitudina l a s oppose d t o a cross-sectiona l stud yan d i t i s important . Wit hthe ful l sampl e o f 6 2 children , the relativel yhigh preschoo l inde xo f exposur e wa s no t significantl yrelate d t o an y late r outcome measure . I objec t t o th e statemen t o n p.18 , 12t hline fro mthe bottom : "Thes e simpl e logitudina l analyse s provid e suppor t fo r the hypothesi s tha t an increas e i n bloo d Pbfro mage s 4- 5 t o 9-1 0 yrs , i s associate d wit ha decreas e i n I Q ... " Whil e mean I Q change d verylittle , mea nP. 4

'- % ' . -. ' * > lea d leve l droppe d appreciabl yan d veryfe wchildre n actuall y increase d i n lea

d level . Th e us e o f residua l score s i n thi s situatio n lead s t o th e anomalou s situatio n i n whic hactua l decrease s i n lea d leve l ar e identifie d a s increase s i n residua l scor e for mbecaus e they d o no t decreas e t o th e exten t predicte d b yth e regression . It' s interesting t o look a t th e actua l paire d lead level s fo r th e childre n identifie d b

ysubjec t numbe r i n Figur e 1 „ Th e greates t "decrease " i s fo r §5 8 whos e lea

d leve l wa s 1 0 o n bot htime s o f sampling . I n the rang e t o th e righ t o f th e mean , th e same residua l scor e coul d b e obtaine d bot hb

yincreasing o r b

ydecreasing lea

d level , depending o n th e initia l value . Thi s make s sens e fro mwha t w e kno wabou t regres sion , bu t i t i s no t verysensibl e fromthe perspectiv e o f th e perso n needing t o mak e decision s abou t the effect s o f lead . Mos t certainl yth e fac t o f th e dro p i n lea d leve l ove r time shoul d b e brough t int o thi s discussion . Th e statemen t quote d abov e ca n easil yb e misconstrue d b yperson s no t familia r wit hthi s fac t an d wit hth e natur e o f regressio n analysis . Wit hlowcros s lag correlations , it' s har d t o mak e muc hsens e ou t o f th e correlatio n betwee n residuals . I t coul d reflec t anothe r changing conditio n no t include d i n th e covariates , or , perhaps , intra-individua l labilit yo r stability . Onc e agai n though , the mos t importan t problemwit hthi s mode l fo r analysi s o f th e dat a i s tha t i t statisticall yextract s the mos t importan t variable , i.e. , th e preschoo l lea d index .



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