ABSTRACT
This chapter is devoted to review of the application of epidemiological methods to the study of neurotoxic illness in a large number of people. The large majority of human studies in which a neurotoxic dose has been linked to levels of neuropsychological functioning has been performed in the context of epidemiological surveys and with the aid of statistical thinking. Neurological symptoms, particularly depression, were the earliest and most prominent symptoms in Michigan residents exposed to Polybrominated biphenyls. Epidemiological studies sometimes cannot be planned—for example, in epidemiological studies of environmental disasters or occupational accidents. The fundamental difference between epidemiological studies in humans and toxicological experiments in animals is the degree of control of the independent variable. Epidemiological studies, including medical field surveys, are more apt to be called quasi-experiments. The “treatment effects” are studied as they exist, that is, as a result of environmental and/or occupational exposure to toxic agents.
