Epidemiologic study designs allow researchers to investigate the cause of an outcome (disease, illness, or death), as well as exposures and risk factors that lead to the outcome. When done efficaciously, epidemiologic studies allow us to estimate the risk or odds of getting a particular disease, given a set of exposures or risk factors. This knowledge allows researchers to apply their findings to the group under study or to the larger population.
Ecological studies, sometimes called correlational studies, are observational studies that rely on population/group-level data rather than individual-level data. The units of comparison in these types of studies are often countries, family units, or neighborhoods.
A cross-sectional study, sometimes called a prevalence study, is an observational study that collects data on the exposure and the outcome at a specific point in time. A cross-sectional study, allows the researcher to take a “snapshot” of the study population.
Case-control studies are observational studies where the outcome (disease/illness) is measured before the exposure is observed. In case-control studies, both the exposure and the outcome have already occurred. The job of the researcher is to determine which exposure led to the outcome.
Cohort studies are observational studies that compare outcomes (disease/illness) between groups (exposed and unexposed) over time. These types of studies are efficient for rare exposures and can either be retrospective (looking backward in time) or prospective (looking forward in time). In retrospective cohort studies, some participants may already have the outcome of interest, whereas, in prospective cohort studies, the researcher will follow the group until the outcome(s) of interest develop.
An experimental study, sometimes called an intervention study, is a non-observational study where the investigator assigns the exposure (new drug, diet, programs, intervention) to a group and follows the group over time to determine the relationship between the exposure and the outcome.
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