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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. t 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 developmental outcomes t'4. The authors argue that the estimated effects represent causal relationships because their analysis controlled for ten socio- demographic covariates. This conclusion of causality may be praAature, 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 developmental 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 I have repeatedly been found to be strongly related to lead level in poor and working class children ^.uality of child care is also strongly associated with developmental outcome ~, including school performance through adolescence i~ . These confounding effects are conceptually distinct from and only partly accounted for empi rically by socio-demographic variables such as etaternai IQ and parental education which were included as covariates by Needleman et al. The fact, that none of the reported lead effects were attenuated by inclusion of their coveriates, as is usually the case in observational studies of low lead levels, 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 reviewerst2 , 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= 1N, the lead effect I _-1.51 (p = .133, 2- sided); after exclusion, with N='17'1, t = -2.56 (p =.01i). This suggests the presence of high IQ's in the plumbism group. In the present follow-up report, the previously excluded cases who agreed to participate were incorporated in the analysis, including, in separate descriptive summaries, ten of the plumbism cases. Five of these plumbism cases had reading disabilities, and three out of seven failed to graduate high school. These high proportions of adverse outcomes seem to corroborate the hypothesized lead effect. However, in view of the apparently contradictory IQ data described abovp, a susmary of the IQ scores of all 16 plumhism cases would be helpful in assessing the implications of the findings. CCa.zre I EV-k(I.1--~ 1-SLcLtTec-Z u ~ I I -- - ~

References 1. WEeedleman HL, Schell A, Bellinger D, Leviton A, Alired EN. The long term effects of exposure to low doses of lead in childhood. N Eng J h4ed 1990;322: 83-8. 2. FIe,Michael AJ, Baghurst PA, Wigg NR, Vimpani GV, Robertson EF, Roberts F;J. Port Pirie cohort study: Environmental exposure to lead and children's abilities at the age of four years. N Eng J Med_1988;319: 468-75. 3. Fergusson DM, Fergusson JE, Horwood LJ, Kinzett NG. A longitudinal study of dentine lead levels, intelligence, school performance and behaviour II. Dentine lead and cognitive ability. J Child Psychol Psychiatry 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. Csidwell BH, Bradley R. Home Observation for the Measurement of the Environment. Unpublished manuscript. Little Rock: Univ of Arkansas at Little Rock, 1984. 6. Po'lansky NA, Borgman RD, De Saix C. Roots of Futility. San Francisco: Jo:>sey-Bass, 1972. 7. Dis;trich 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 1S185;75:1114-9.

8. Hunt TJ, 64epner R, Seaton KW. Childhood lead poisoning and inadequate child care. Am J Dis Child 1982;136:538-542. 9. Bradley RH, Caidwell BM, Rock SL, Ramey CT, Barnard KE, Gray C, Hanrrtond MA, Mitchell S, Gottfried AW, Siegel L, Johnson DL. Home environment and cognitive development in the first 3 years of life: A collaborative study involving six sites and three ethnic groups in North 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: ,5i3 Schroeder (Ed.) Toxic Substances and Mental Retardation: Idourobehavioral Toxicology and Teratology. Washington, D.C.: AAMD Monograph Series, 1987 12. Nffaedleman HL, Gunnoe C, Leviton A, Reed R, Peresie H, Maher C, Barrett P. (1979). Deficits in psychological and classroom performance in children with elevated dentine lead levels. N Eng J Med 1979;300: BE~ 9-95 . 13. US Environmental Protection Agency. Independent peer review of selected studies concerning neurobehavioral effect of lead exposures i'n nominally asymptomatic children: Official report of findings and recortrnendations of an interdisciplinary expert review cornnittee. (EPA-600/8-83-028A). 14. Needleman HL. Appendix to the ECAO critique. Unpublished manuscript, on file with the Environmental Protection Agency, 1984.