METHODS OF EPIDEMIOLOGICAL STUDIES
The methods of epidemiological studies are presented in Fig. 6.1.
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Figure 6.1. The methods of epidemiological studies
Epidemiological studies are aimed, where possible, at revealing unbiased relationships between exposures such as alcohol or smoking, biological agents, stress or chemicals to mortality or morbidity. The identification of causal relationships between these exposures and outcomes is an important aspect of epidemiology. Modern epidemiologists use informatics as a tool.
Descriptive observations (ecological studies) pertain to the «who, what, where and when» of a health-related event. However, analytical observations deal more with the «how» of a health-related event. An ecological study does not link individual outcome events to individual exposure or confounding characteristics, and it does not link individual exposure and confounding char-
acteristics to one another. In an ecological study, information about exposure and disease is available only for groups of people and critical information can be lost in the process of aggregating these data. The results of ecological studies are difficult to interpret, and serious errors can result when it is assumed that inferences from an ecological analysis pertain either to the individuals within the group or to individuals across the groups.
Analytical studies can provide the necessary information to help evaluate the causality of an association and estimate the magnitude of risk. For each person included in the study, information is obtained about their disease status, their exposure to various contaminants and confounding characteristics.
Cross-sectional study. Exposure and disease information relate to the same period; in these studies, it may not always be correct to presume that exposure preceded disease. This study reflects the state of the groups studied at a given time, so they are often called «sectional studies» or «simultaneous studies».