Improving Causal Inference: Strengths and Limitations of Natural Experiments

By Dunning, Thad | Political Research Quarterly, June 2008 | Go to article overview

Improving Causal Inference: Strengths and Limitations of Natural Experiments


Dunning, Thad, Political Research Quarterly


Social scientists increasingly exploit natural experiments in their research. This article surveys recent applications in political science, with the goal of illustrating the inferential advantages provided by this research design. When treatment assignment is less than "as if" random, studies may be something less than natural experiments, and familiar threats to valid causal inference in observational settings can arise. The author proposes a continuum of plausibility for natural experiments, defined by the extent to which treatment assignment is plausibly "as if" random, and locates several leading studies along this continuum.

Keywords: natural experiment; "as if" random; exogenous variation; continuum of plausibility; matching

If I had any desire to lead a life of indolent ease, I would wish to be an identical twin, separated at birth from my brother and raised in a different social class. We could hire ourselves out to a host of social scientists and practically name our fee. For we would be exceedingly rare representatives of the only really adequate natural experiment for separating genetic from environmental effects in humans-genetically identical individuals raised in disparate environments.

-Stephen Jay Gould (1996, 264)

1. Introduction

Social scientists are increasingly exploiting natural experiments in their research. A recent search on "natural experiment" using "Google Scholar" (scholar .google.com) turned up more than 1 million hits; the results appearing on the first dozen pages suggest that economics and epidemiology are the leading fields to use the term, but political science is also well represented. An impressive volume of unpublished, forthcoming, and recently published studies in political science suggests the growing influence of the natural experimental approach. Table 1 provides a nonexhaustive list of several recent studies.

As the name suggests, natural experiments take their inspiration from the experimental approach. A randomized controlled experiment (Freedman, Pisani, and Purves 1997, 4-8) has three hallmarks. First, the response of experimental subjects to a "treatment" (or a series of treatments) is compared to the response of other subjects to a "control" regime, often defined as the absence of a treatment. Second, the assignment of subjects to treatment and control groups is done at random. Third, the application or manipulation of the treatment is under the control of the experimental researcher. Each of these traits plays a critical role in the experimental model of causal inference. For example, in a medical trial of a new drug, the fact that subjects in the treatment group take the drug, while those in the control group do not, allows for a comparison of health outcomes across the two groups. Random assignment ensures that any difference in average outcomes between the two groups is not due to confounders, or factors other than the treatment that vary across the two groups and that may explain differences in health outcomes. Finally, experimental manipulation of the treatment establishes evidence for a causal relationship between the treatment and the health outcomes.1

Unlike true experiments, the data used in natural experiments come from naturally occurring phenomena-actually, in the social sciences, from phenomena that are often the product of social and political forces. Because the manipulation of treatment variables is not generally under the control of the analyst, natural experiments are, in fact, observational studies. However, unlike other nonexperimental approaches, a researcher exploiting a natural experiment can make a credible claim that the assignment of the nonexperimental subjects to treatment and control conditions is "as if" random. Outcomes are compared across treatment and control groups, and both a priori reasoning and empirical evidence are used to validate the assertion of randomization. Thus, random or "as if" random of assignment to treatment and control conditions constitutes the defining feature of a natural experiment. …

The rest of this article is only available to active members of Questia

Sign up now for a free, 1-day trial and receive full access to:

  • Questia's entire collection
  • Automatic bibliography creation
  • More helpful research tools like notes, citations, and highlights
  • Ad-free environment

Already a member? Log in now.

Notes for this article

Add a new note
If you are trying to select text to create highlights or citations, remember that you must now click or tap on the first word, and then click or tap on the last word.
One moment ...
Default project is now your active project.
Project items

Items saved from this article

This article has been saved
Highlights (0)
Some of your highlights are legacy items.

Highlights saved before July 30, 2012 will not be displayed on their respective source pages.

You can easily re-create the highlights by opening the book page or article, selecting the text, and clicking “Highlight.”

Citations (0)
Some of your citations are legacy items.

Any citation created before July 30, 2012 will labeled as a “Cited page.” New citations will be saved as cited passages, pages or articles.

We also added the ability to view new citations from your projects or the book or article where you created them.

Notes (0)
Bookmarks (0)

You have no saved items from this article

Project items include:
  • Saved book/article
  • Highlights
  • Quotes/citations
  • Notes
  • Bookmarks
Notes
Cite this article

Cited article

Style
Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

(Einhorn, 1992, p. 25)

(Einhorn 25)

1

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited article

Improving Causal Inference: Strengths and Limitations of Natural Experiments
Settings

Settings

Typeface
Text size Smaller Larger Reset View mode
Search within

Search within this article

Look up

Look up a word

  • Dictionary
  • Thesaurus
Please submit a word or phrase above.
Print this page

Print this page

Why can't I print more than one page at a time?

Full screen

matching results for page

Cited passage

Style
Citations are available only to our active members.
Sign up now to cite pages or passages in MLA, APA and Chicago citation styles.

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn, 1992, p. 25).

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences." (Einhorn 25)

"Portraying himself as an honest, ordinary person helped Lincoln identify with his audiences."1

1. Lois J. Einhorn, Abraham Lincoln, the Orator: Penetrating the Lincoln Legend (Westport, CT: Greenwood Press, 1992), 25, http://www.questia.com/read/27419298.

Cited passage

Thanks for trying Questia!

Please continue trying out our research tools, but please note, full functionality is available only to our active members.

Your work will be lost once you leave this Web page.

For full access in an ad-free environment, sign up now for a FREE, 1-day trial.

Already a member? Log in now.