EPIDEMIOLOGIC APPROACHES TO ASSESSING THE DEVELOPMENTAL TOXICITY OF LEAD

A variety of designs have been employed in epidemiologic studies of th e developmental morbidity associated with low-level lead exposure. His torically, cross-sectional and retrospective cohort designs have been used most frequently. Despite improvements in their methodological rig or, however, certain design features constrain the inferences such stu dies can support. These limitations stem from the substantial risk tha t children's exposure status may be misclassified due to reliance on i ndices with short averaging times, and an inability to identify either age-related changes in vulnerability or time-dependent aspects of the expression of toxicity (e.g., reversibility). In response to these li mitations, several studies were initiated involving repeated measureme nts of children's lead exposure and development over periods as long a s a decade. Although these prospective studies are characterized by an unusual degree of coordination among the investigators, there are dif ferences among them as well, most notably in terms of sample character istics and patterns of exposure. As a result, the studies should be vi ewed as complementary rather than simply as replicates of one another. Moreover, like all epidemiologic approaches the prospective design ha s its own limitations. These include the need to maintain follow-up ov er a long period of time, as well as the attendant risk of bias in sam ple attrition, and the need to distinguish developmental effects of le ad from psychometric artifacts. The Boston prospective study is used t o illustrate both the strengths and weaknesses of the prospective desi gn. (C) 1993 Intox Press, Inc,