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Th e L.L . Thurston e Psychometri cLaboratory TH EUNIVERSIT YO FNORTHCAROLINA AT CHAPELHILL
Januar y8 , 198 5 TheUniversityof NorthCarolin aa

tChapelHill Davi eHall01 3 A ChapelHill . N.C . 2751 4

MEMORANDU M TO : Joh nHaines , Chie f Ambien t Standard s Branch , Sectio nB FROM : Thoma s S . Wallstenl^ Q RE : Developmen t o f I Q Protoco l andselectio no f consultant s Th e purpos e o f thi s memorandumi s t o describ e th e proces s b y whic hw e hav e develope d th e protoco l fo r encodin g probabilisti c judgment s abou t lead-induce dI Q decrements , andt o indicat e whic h expert s w e hav e consulted . Ou r origina l intentio nwa s t o develo p a protoco l analogou s t o th e on e fo r hemoglobi ndecrement , accordin g t o whic hw e woul d encod e experts ' probabilisti c judgment s abou t dose-respons e func
tion s fo r lead-induce d I Q decrements . However , a s wil l b e de
scribe d i nthi s memorandum , th e natur e o f th e uncertaintie s i s vastl ydifferen t i nth e tw o cases , anda nentirel ydifferen t protoco l i s required . Instea do f askin g abou t dose-respons e functions , w e wil l pos e idea l hypothetica l experiment s andas k abou t thei r outcomes . Th e probabilisti c response s t o thes e ques tion s wil l the nb e use d t o estimat e probabilitie s abou t dose
respons e function s and abou t mea ndose-effec t functions . I npreparin g t o develo p th e protoco l w e initiall yrea dth e draf t Criteri a Documen t (CD ) andconsulte dwit hsuitabl e experts , som e o f who m

ha d aide d i nwritin g th e releven t portion s o f th e C D and al l o f who mha d publishe d researc ho nneural , behavioral , o r cognitiv e effect s o f lead . Thes e expert s wer e Drs . Verno n Benignus , Rober t Bornshein , Ki mDietrich , Davi dOtto , andStephe n Schroeder . W e the ndevelope d a firs t draf t o f a nI Q protocol . I t wa s designe d t o elici t probabilisti c judgment s abou t dose-respons e curve s fo r advers e effect s define di nterm s o f I Q decrements . Fo r example , a nI Q decremen t o f 2 point s o r o f 7 point s migh t b e specified , and th e dose-respons e curv e woul dindicat e th e per centag e o f th e populatio nwh o suffer s a t leas t tha t decremen t a t eac hlea d dos e level . Th e protoco l wa s designe dt o elici t proba
bilisti c judgment s abou t thi s curve .P. 3 

# T Mr . Joh nHaine s Januar y8 , 198 5 Pag e 2 Thi s draf t wa s discusse dwit hmos t o f th e expert s mentione d abov e a s wel l a s wit ha numbe r o f others . Th e consultant s uti
lize d a t thi s poin t wer e Drs . Verno nBenignus , Clair e Ernhart , Leste r Grant , Lloyd Humphries , Lyl e Jones , Herber t Needleman , Davi d Otto , Stephe nSchroeder , and Bernar dWeiss . Thei r re sponse s wer e generall yfavorabl e andver yconstructive . However , i ndiscussin g wit hthes e peopl e ho wthe ywoul dthin k abou t and respon d t o th e question s i nth e protocol , tw o factor s becam e apparent . First , althoug hth e concep t o f a dose-respons e curv e her e i s wel l defined , i t i s no t commonl yuse di nthi s context . Thi s i s becaus e I Q decrement s canno t b e observe ddirectly , bu t ca nonl y b e inferre d statistically . Furthermore , th e matte r i s s o comple x tha t th e -statistic s ar e no t a t al l simple . Th e secon dfacto r wa s tha t i nattemptin g t o respon d t o th e questions , th e expert s wer e envisionin g hypothetica l experiments , considerin g wha t th e out come s migh t be , and the nextrapolatin g fro mtha t t o th e dose
respons e function s o f interest . I t seeme d t o m e tha t i t woul d b e fa r mor e consisten t wit h th e expert s usua l wa yo f thinkin g andb e easie r fo r the mt o respon d i f w e encode d directl ythei r probabilisti c judgment s abou t outcome s o f suitabl e hypothetica l experiments . I naddi
tion , byproperl ydesignin g thes e hypothetica l experiments , w e coul d eliminat e th e nee d t o worr yabou t som e o f th e complexitie s tha t aris e i nactua l research . W e coul dthe nd o th e extrapola
tion s mathematicall ytha t the ywer e tryin g t o d o mentally . Accordingly , a ne wversio no f th e protoco l wa s develope dt o elici t probabilisti c judgment s abou t th e outcome s o f idea l hypo
thetica l experiments . Thi s protoco l als o indicate dho wth e judg
ment s woul d b e use d and th e assumption s tha t woul db e incorpo
rate d i nworkin g wit hthem . Th e ne wdraf t wa s discusse d wit hDrs . Verno nBenignus , Anit a Curan , Clair e Ernhart , LloydHumphries , Lyl e Jones , Marc y Lansman , Herber t Needleman , Davi dOtto , andStephe nSchroeder . The yfoun d i t muc heasie r and mor e natura l t o respon dt o thi s versio ntha nt o th e previou s one . However , variou s comment s lea d t o a thir d draf t o f th e protoco l incorporatin g a nimprove didea l hypothetica l experimenta l design . Thi s draf t wa s discusse dwit h mos t o f th e peopl e wh o ha d see nth e previou s one , andsom e ver y mino r change s wer e made . Th e protoco l wa s the nuse dwit htw o pilo t subjects , on e an EP Aenvironmenta l healt hscientis t an dth e othe r a psycholog y graduat e studen t doin g a relate ddissertation . Th e judgmenta l probabilit yencoding s wen t ver ywell . However , i nanalyzin g th e judgment s and discussin g thes e analyse s wit hDr . Lyl e Jones , w e recentl ynotice d tha t certai nadditiona l judgment s wer e needed . Th e protoco l i s no wstructure di na wa ytha t ou r consultant s conside r reasonabl e an d i nwhic hthe ywoul dfee l comfortabl e providin g th e desire d probabilisti c judgments . Th e additiona lP. 4

Mr . JohnHaine s Januar y8 , 198 5 Pag e 3

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••# > judgment s wil l b e obtaine d wit ha ver ymino r chang e i nth e proto col . Nevertheless , th e fina l versio no f th e protoco l wil l b e discusse d wit ha subse t o f th e peopl e wh o sa wth e previou s on e t o assur e tha t th e chang e i s acceptable . cc : J . Cohe n T . Feagan s R . Whitfiel d