Summary
Scientists, justifiably conservative in their approach to causal inference, emphasize avoiding Type I errors. Less attention is given to avoiding Type II errors. Many of the recent reviews and studies of lead at low dose and children’s neurodevelopment have committed Type II errors in evaluation. Among the more common errors encountered are the following: (1) treating the criterion p = 0.05 as a sacrament; (2) positing phantom confounders; (3) constructing false causal models; (4) making no-effect inferences from samples too small to give adequate power; (5) underestimating the importance of ‘small’ differences between groups; (6) examining each study in isolation; and (7) requiring proof of causality.
The power of many studies was surprisingly small, due to sample size and the number of covariates controlled. The effect sizes of the differences between exposed and non-exposed groups was 0.4 studies occuring by the chance was 3 x 10-1. These findings converge stongly on the conclusion that lead at low dose is neurotoxic. they also provide guidlines for future studies of the question.
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Needleman, H.L., Bellinger, D.C. (1989). Type II Fallacies in the Study of Childhood Exposure to Lead at Low Dose: A Critical and Quantitative Review. In: Smith, M.A., Grant, L.D., Sors, A.I. (eds) Lead Exposure and Child Development. Springer, Dordrecht. https://doi.org/10.1007/978-94-009-0847-5_17
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DOI: https://doi.org/10.1007/978-94-009-0847-5_17
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