Behavioral teratology/toxicology: How do we know what we know?

Knowledge about human behavioral teratology/toxicology must necessarily be limited by the methods that can ethically be used. Research in the field is an enterprise calling for tolerance for uncertainty if not chaos. Among th e main points of this paper are: (a) Kaufman's criticisms of research on lo w blood-lead level (BLL) and children's IQ are generally valid and apply to virtually all human natural-groups research; (b) Relative to some contexts , research on low BLL on children's IQ is exemplary; (c) Relative to other contexts, the conclusion that low BLL have linear effects is well supported ; (d) Owing to necessary design limitations, all natural-groups studies hav e shortcomings; (e) Inference of causality is uncertain under any condition s; and (f) Some authors readily leap from molehills of data to mountains of causal conclusions. (C) 2001 National Academy of Neuropsychology. Publishe d by Elsevier Science Ltd.