What is an observational study?

Abstract

Observational studies are a fundamental part of epidemiological research. They are called observational studies because the investigator observes individuals without manipulation or intervention. This is in contrast to randomised controlled trials where investigators do intervene and look at the effects of the intervention on an outcome. Although randomised controlled trials are useful in determining causal relationships between treatment and outcome, there are often instances where randomised controlled trials are not appropriate, so observational studies are needed. Randomised controlled trials have to be ethical, but often there are questions that it would be unethical to do a trial on. For example, if one wanted to conduct a hypothetical trial to determine if smoking caused lung cancer, individuals would be randomized to smoke or not smoke, and then followed up until death to subsequently determine the effect of smoking on lung cancer. Observational studies can determine if there are