The Epidemiologic Approach

Epidemiological studies rarely provide unequivocal data on the effects of toxic substances on human health. Unlike experimental studies, pertinent variables frequently cannot be controlled and some are often unknown. Nevertheless, these limitations can be dealt with by various facets of an epidemiological investigation. These include, the choice of a study design, selection of controls or comparison populations, evaluation of available data, statistical analysis, and the drawing of appropriate inferences from the data. Among the special problems that might be encountered in studies of the effects of cardiotoxic substances are, difficulties in establishing diagnoses, errors in death certificates, observer errors in electrocardio-graphic interpretations, and taking into account the effects of various risk factors known to be implicated in the etiology ofcardiovascular diseases. In spite of various methodological problems and certain inherent limitations of epidemiological studies, they can, when properly conducted, make significant contributions to knowledge of disease etiology and provide the means of reducing the risk of a disease, even when its etiology is not completely known. When a particular chemical compound is found to be toxic to animals, data on the nature and extent of that chemical's toxicity to humans are frequentl