FIGURE 1-1 Sources of evidence for inferring whether exposures from hazardous-waste sites cause an impact on public health.

  1. Knowledge of symptomatology or disease occurrence has in some instances been derived from studies of populations exposed to hazardous-waste sites. Often, these have not described exposures accurately, or they have failed completely to identify a specific causal factor. Nevertheless, with the knowledge that is available about exposure elsewhere, and from the knowledge that some of these exposures can result in the observed symptomatology or diseases found in excess in those exposed to hazardous-waste sites when compared to suitable controls, sufficient indirect evidence of causality might have been accumulated to justify remedial action for purposes of protecting public health.

In adopting the above framework, the committee does not follow the approach traditionally used by epidemiologists in deriving inferences of causality (Hill, 1953; USDHHS, 1976). Historically, discussions on causality have proceeded once a statistically significant relationship between a potential causal factor and a disease has been found, as is discussed below. However, what constitutes the best



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