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Letter to the New England Journal of Medicine [September, 19901 To the Editors: In their January 11 article Needleman et al. 1 report strikingly large effects of low lead levels on several late adolescence outcomes. For example, an estimated 7.4-fold increased odds of school failure was attributed to childhood lead dentin levels above 20 ppm. Such massive effects sizes contrast sharply with results of other studies relating low lead level to earlier develoFoental outcomes The authors argue that the estimated effects represent causal relationships because their analysis controlled for ten socio- demogra,phic covariates. This conclusion of causality may be premature, however, because the covariate set did not include measures of the quality of child care (i.e., parental responsitivity, involvement with the child, provision of books, suitable playthings, etc.), a primary confounder in previous studies of developrmantal lead effects. Thus the reported lead effects may be partly due to spurious association Induced by variations in the caretaking environment. Indices of child care quality such as the HOME S and the CLL 6 have repeatedly been found to be strongly related to lead level in poor and working class children~~4~~~8 . Quality of child care is also strongly associated with developmm.,ntal outcome 9, including school performance through adolescence 10 . These confounding effects are conceptually distinct from and only partly accounted for empirically by socio-demographic variables such as maternal IQ and parental educatior,~~ , which were included as covariates by Needleman et al. The fact that none of the reported lead effects were attenuated by inclusion of their covari ate,s, as i s usuall y the case i n observat i onal studi es of l ow l ead l evel s, indicates that confounders such as child care may not have been fully controlled. On another matter, the present report is a follow-up of a 1979 report 12 which troubled reviewers13 , in part, because many cases were excluded aFter testing. In a written response to the review 14, Needleman reported data indicating that a key IQ analysis was substantially affected by 16 of the

excluded children with excess lead, or plumbism: Prior to exclusion, with N= 187, the lead effect t=-1.51 (p =.133, 2 - sided); after exclusion, with N= 171, t=-2.56 (p =.011). This suggests the presence of high IQ's in the plumbiwn group. In the present follow-up report, the previously excluded cases who agreed to participate were incorporated in the analysis, including, in separatE3 descriptive summaries, ten of the plumbism cases. Five of these plumbim cases had reading disabilities, and three out of seven failed to gradua'tES high school. These high proportions of adverse -~utcomes seem to corroborate the hypothesized lead effect. However, in view of the apparently contradictory IQ data described above, a summary of the IQ scores of all 16 plumbism cases would be helpful in assessing the implications of the findings. (41o .~ 4aw7'.'^'CL^

References 1. Needleman HL, Schell A, Bellinger D, Leviton A, Allred EN. The long term effects of exposure to low doses of lead in childhood. N Eng J Med 1990;322: 83-8. 2. McMichael AJ, Baghurst PA, Wigg NR, Vimpani GV, Robertson EF, Roberts RJ. Port Pirie cohort study: cnvironmental exposure to lead and children's abilities at the age of four years. N Eng J Med 1988;319: 468-•75. 3. Fea-c,~usson DM, Fergusson JE, Horwood LJ, Kinzett NG. A longitudinal study of dentine lead levels, intelligence, school performance and behEiviour II. Dentine lead and cognitive ability. J Child Psychol Psyc,hi atry 1988 ; 29:793-809. 4. Ernhart CB, Morrow-Tlucak M, Wolf AW, Super D, Drotar D. Low level lead exposure in the prenatal and early preschool periods: Intelligence prior to school entry. Neurotoxicol Teratol 1989;11: 161-170. 5. Caldwell BM, Bradley R. Home Observation for the Measurement of the Environment. Unpublished manuscript. Little Rock: Univ of Arkansas at Little Rock, 1984. 6. Polansky NA, Borgman RD, De Saix C. Roots of Futility. San Francisco: Jossey-Bass, 1972. 7. Dietrich KN, Krafft KM, Pearson DT, Harris LC, Bornschein RL, Hammond PB, Succop PA. Contribution of social and developmental factors to lead exposure during the first year of life. Pediatrics 1985;75:1114-9.

• 8. Hunt TJ, Hepner R, Seaton KW. Childhood lead poisoning and inadequate child care. Am J Dis Child 1982;136:538-542. 9. Bra,dley RH, Caldwell BM, Rock SL, Ramey CT, Barnard KE, Gray C, Haunrnond MA, Mitchell S, Gottf ried AW, Siegel L, Johnson DL. Home environment and cognitive development in the first 3 years of life: A callaborative study involving six sites and three ethnic groups in Ncrth America. Dev Psychol 1989;25:217-35. 10. Hess RD, Holloway SD. Family and school as educational institutions. In: Parke RD, ed. The Family. Chicago: Univ. Chicago Press, 1984. 11. Schroeder SR, Hawk B. Psycho-social factors, lead exposure and IQ. In: SR Schroeder (Ed.) Toxic Substances and Mental Retardation: Neui^obehavioral Toxicology and Teratology. Washington, D.C.: AAMD Monograph Series, 1987 12. Needleman HL, Gunnoe C, Leviton A, Reed R, Peresie H, Maher C, Barrett P. 1;1979). Deficits in psychological and classroom performance in chilidren with elevated dentine lead levels. N Eng J Med 1979;300: 689- 95. 13. US Environmental Protection Agency. Independent peer review of sellected studies concerning neurobehavioral effect of lead exposures in rominally asymptomatic children: Official report of findings and recommendations of an interdisciplinary expert review committee. (EF'A-600/8-83-028A). 14. Needleman HL. Appendix to the ECAO critique. Unpublished manuscript, on file with the Environmental Protection Agency, 1984.