Subclinical Lead Level and Developmental Deficit: Re-Analyses of Data

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Abstract
Perino and Ernhart (1974) reported that moderate levels of lead exposure in 80 preschool urban black children were related to cognitive impairment. Ernhart, Landa, and Schell (1981) re-examined 63 of these children five years later and found no significant association of preschool lead level and outcome measures—including cognitive measures, reading tests, and teacher behavior ratings. School-age lead level was marginally related to a few measures. After review of methodological issues, it was concluded that if these results were due to lead, the effect was minimal. Since the issue is important to the task of the Environmental Protection Agency (EPA), EPA appointed an Expert Committee to examine these reports and those of another person whose work has been questioned. Some data re-analyses were requested. The previously reported positive findings of the preschool study were not substantiated in re-analysis. The school-age lead data required technical adjustment. Additional variables were generated including change scores, combinations, and interactions. Out of 66 analyses, two tests of the lead effect were significant. The first depended on a deviant case; the second was an uninterpretable interaction. It was concluded that if these results are due to a lead effect, the effect is minimal. The most important result was unchanged; there was no evidence of an effect of moderate blood lead levels in the preschool period and any school-age outcome measure.