Overview of Study Designs

Study designs are used by epidemiologists to collect and study information when testing hypotheses. Epidemiologists use different methods to study the course of a disease starting from exposure to a risk factor. Experimental studies, also known as trials, investigate the role of some factor or agent in the prevention or treatment of a disease. Experimental studies are thought to produce the most scientifically rigorous data of all the designs. However, experimental studies are often difficult to perform because of problems with enrolling participants, high costs, and ethical issues. Therefore, most epidemiological studies are observational studies.

Observational studies occur when researchers observe events for individuals in the study without altering them. Observational studies are considered "natural" experiments because the investigator lets nature take its course. Observational studies are not limited to preventions and treatments and do not suffer from the ethical and feasibility issues of experimental studies. Experimental studies investigate whether a measure prevents disease occurrence (prophylactic) or treats an existing condition (clinical). In the following pages we will learn about cohort studies, cross-sectional studies, case-control studies, and ecological studies.

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