Environmental lead and children's intelligenceBMJ 1995; 310 doi: https://doi.org/10.1136/bmj.310.6991.1408a (Published 27 May 1995) Cite this as: BMJ 1995;310:1408
Studies included in the meta-analysis are not representative
- Herbert L Needleman
- Professor of psychiatry and paediatrics Western Psychiatric Institute and Clinic, University of Pittsburgh Medical Center, Pittsburgh, PA 15213-2593, USA
EDITOR,—Stuart J Pocock and colleagues' metanalysis of 26 studies of asymptomatic exposure to lead in children concludes that “the evidence strongly supports an inverse association between body lead burden and child IQ.”1 The authors then urge caution before the relation is accepted as causal. They do this on the basis of the following considerations: Are the studies representative? Is confounding adequately dealt with? Is selection bias at work? Is causality reversed: does low IQ cause ingestion of lead?
These questions have been asked and answered before. The criticism of non-representativeness could readily be applied to Pocock andcolleagues' analysis, which includes …