Natural Experiment

A natural experiment is an observational study that takes advantage of a naturally occurring event or situation that can be exploited by a researcher to answer a particular question. Natural experiments are often used to study situations in which a true experiment is not possible, for instance, if the exposure of interest cannot be practically or ethically assigned to research subjects. Situations that may create appropriate circumstances for a natural experiment include policy changes, weather events, or natural disasters. This entry describes natural experiments, examines the limitations to such experiments that exist as a result of confounding, and discusses the use of instrumental variables to control confounding.

The key features of experimental study designs are manipulation and control. Manipulation, in this context, means that the experimenter ...