<P> Epidemiologists employ a range of study designs from the observational to experimental and generally categorized as descriptive , analytic ( aiming to further examine known associations or hypothesized relationships ) , and experimental ( a term often equated with clinical or community trials of treatments and other interventions ) . In observational studies , nature is allowed to `` take its course , '' as epidemiologists observe from the sidelines . Conversely , in experimental studies , the epidemiologist is the one in control of all of the factors entering a certain case study . 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 . </P>
epidemiologists attempt to explain the link between health and variables such as
biological agents stress chemicals alcohol smoking