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Correspondence: The Melatonin Hypothesis: A Matter of Method

Environmental Health Perspectives
Environmental Health Perspectives
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110(2) FrontPages PCB-Induced Impairments in Older Adults: Critique of Schantz et al.’s Methodology and Conclusions Shantz (1) provided a valuable scientific ser- vice to the field of the developmental neu- rotoxicity of polychlorinated biphenyls (PCBs) by offering insightful criticisms of the methodologies used by Jacobson et al. (2) and others. Schantz and colleagues pro- ceeded to study PCBs and dichlorodiphenyl dichloroethane (DDE), shifting the focus from effects on infants and children to effects on a cohort of older adults (3–6). The shortcomings of the research design and data analysis used by Shantz et al. are equivalent to the shortcomings of previous studies (1). In their paper published in 2001 (3), Schantz et al. a) failed to account adequately for the chance significant find- ings that occur when many statistical analy- ses are conducted simultaneously; b) used an outdated measure of memory when a much-improved test was available at the time of testing; c) failed to consider the implications of the experimental inter- dependency of two key variables that were significantly related to PCBs; and d) con- trolled IQ (intelligence quotient) only with the Wechsler Adult Intelligence Scale- Revised (WAIS-R) vocabulary subtest. Schantz et al. (3) conducted 48 multi- ple regression analyses simultaneously, 24 with DDE and 24 with PCBs, spanning several cognitive domains. They used an alpha level of 0.05, which means that one significant finding is expected to occur by chance alone for every 20 analyses; with 48 analyses, 2–3 significant findings will occur by chance. Schantz et al. identified four sig- nificant findings, which is barely above the number expected by chance; however, they focused only on three—the ones that pro- duced the anticipated negative correla- tion—and they virtually ignored the signif- icant, but opposite, relationship between DDE and delayed recall. Of the three nega- tive associations with PCBs, two were experimentally interdependent—List A, Trial 1, and

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