INTERPRETING THE LITERATURE ON LEAD AND CHILD-DEVELOPMENT - THE NEGLECTED ROLE OF THE EXPERIMENTAL SYSTEM

Controversy over lead's effect on children's cognition rests in part o n the assumption that if such an effect exists it can be characterized by a single estimator (e.g., the same rate of decline in IQ with incr easing exposure, the same neuropsychological presentation), which will be found by any study that is valid. Accordingly, efforts to resolve inconsistencies in study findings have focused almost exclusively on d ata analytic issues germane to bias, in particular confounding and its statistical control. Relatively little consideration has been given t o the role of effect modification, i.e., the impact on effect estimati on of differences in the ''experimental systems'' employed in human ep idemiological studies. Lack of consistency in findings could be due to differences among study cohorts in exposure/toxicokinetic factors (e. g., dose, timing), differences in environmental characteristics (e.g., co-exposures, co-morbidity, developmental supports, assessment settin g), or differences in the distribution of genetic characteristics that affect lead metabolism. Recent findings regarding lead's impact on th e development of nervous system structure and function are consistent with the hypothesis that contextual factors affect the form in which l ead toxicity is expressed and may contribute to the failure to date to identify a lead-associated ''behavioral signature.'' Characterizing t he neuropsychological effects of lead might be facilitated by greater use of a clinical ''process'' approach to assessment, which would perm it the type of fine-grained analyses of lead-associated performance di fferences often employed in studies of behavioral toxicity in animal m odels.