Editing Natural experiment (section)

{{Short description|Empirical study}}
{{Use dmy dates|date=March 2020}}

A '''natural experiment''' is a study in which individuals (or clusters of individuals) are exposed to the [[experiment]]al and [[scientific control|control]] conditions that are determined by [[nature]] or by other factors outside the control of the investigators. The process governing the exposures arguably resembles [[random assignment]]. Thus, natural experiments are ''[[observational studies]]'' and are not [[scientific control|controlled]] in the traditional sense of a [[randomized experiment]] (an ''intervention study''). Natural experiments are most useful when there has been a clearly defined exposure involving a well defined subpopulation (and the absence of exposure in a similar subpopulation) such that changes in outcomes may be plausibly attributed to the exposure.<ref name="DiNardo" >{{cite book|last=DiNardo|first=J.|author-link=<!-- John DiNardo -->|chapter=Natural experiments and quasi-natural experiments|title=The New&nbsp;Palgrave Dictionary of Economics|editor1-first=Steven&nbsp;N.|editor1-last=Durlauf|editor1-link=Steven N. Durlauf|editor2-first=Lawrence&nbsp;E<!-- . -->|editor2-last=Blume|editor2-link=Lawrence E. Blume|publisher=Palgrave Macmillan|year=2008|edition=Second|pages=856–864|chapter-url=http://www.dictionaryofeconomics.com/article?id=pde2008_N000142|doi=10.1057/9780230226203.1162|title-link=New Palgrave|isbn=978-0-333-78676-5}}</ref><ref name=":0">{{cite book |last=Dunning |first=Thad |year=2012 |title=Natural Experiments in the Social Sciences: A Design-Based Approach |publisher=Cambridge University Press }}</ref> In this sense, the difference between a natural experiment and a non-experimental observational study is that the former includes a comparison of conditions that pave the way for [[causal inference]], but the latter does not.

Natural experiments are employed as [[study design]]s when controlled [[experiment]]ation is extremely difficult to implement or unethical, such as in several research areas addressed by [[epidemiology]] (like evaluating the health impact of varying degrees of exposure to [[ionizing radiation]] in people living near Hiroshima at the time of the atomic blast<ref>{{cite book |last=Friedman |first=G. D. |year=1980 |title=Primer of Epidemiology |edition=2nd |location=New York |publisher=McGraw-Hill |isbn=978-0-07-022434-6 |url-access=registration |url=https://archive.org/details/primerofepidemio00frie }}</ref>) and [[economics]] (like estimating the economic return on amount of schooling in US adults<ref>{{cite journal |last1=Rosenzweig |first1=M. R. |last2=Wolpin |first2=K. I. |year=2000 |title=Natural 'Natural Experiments' in Economics |journal=[[Journal of Economic Literature]] |volume=38 |issue=4 |pages=827–874 |doi=10.1257/jel.38.4.827 }}</ref>).<ref name="DiNardo" /><ref name=":0" />