Compare methods

	Regression Discontinuity in Elections	Difference-in-Differences
Field	Political Science	Econometrics
Family	Process / pipeline	Regression model
Year of origin	2008	1994
Originator	David S. Lee (electoral application); broader RD tradition	Card & Krueger (canonical 1994 application); Angrist & Pischke (textbook treatment)
Type	Quasi-experimental causal design using a vote-share threshold	Causal inference / panel regression
Seminal source	Lee, D. S. (2008). Randomized Experiments from Non-random Selection in U.S. House Elections. Journal of Econometrics, 142(2), 675–697.	Angrist, J. D., & Pischke, J.-S. (2009). Mostly Harmless Econometrics: An Empiricist's Companion. Princeton University Press. ISBN: 978-0691120355
Aliases	Close-election RD, Electoral regression discontinuity, Vote-share RD design, Incumbency-advantage RD	diff-in-diff, DiD, Farkların Farkı (Diff-in-Diff)
Related	3	5
Summary	Regression discontinuity in elections is a quasi-experimental design that exploits the sharp winning threshold in electoral contests to estimate causal effects of holding office. Just above the threshold a candidate or party wins; just below, it loses. In very close races, which side ends up just over the line is plausibly as good as random, so comparing the later outcomes of bare winners and bare losers identifies the causal effect of winning — most famously the incumbency advantage — without confounding by candidate or district quality.	Difference-in-Differences is a causal-inference method that estimates the effect of an intervention by comparing how a treatment group and a control group change over time. Made famous by Card and Krueger's 1994 minimum-wage study and developed in Angrist and Pischke's Mostly Harmless Econometrics, it isolates the treatment effect as the difference between the two groups' before-after changes.