Scandinavian Working Papers in Economics

Working Paper Series,
IFAU - Institute for Evaluation of Labour Market and Education Policy

No 2026:19: A double-differences approach to inference in regression discontinuity designs with a discrete running variable

Georg Graetz () and Mattias Nordin ()
Additional contact information
Georg Graetz: Department of Economics, Uppsala University
Mattias Nordin: Department of Statistics, Uppsala University

Abstract: We present a new approach to nonparametric inference in regression discontinuity designs where the running variable is discrete and may have few support points. The approach is based on an intuitive and comparatively weak identification assumption: In the absence of treatment, the difference in population mean outcomes at the cutoff is not the largest nor the smallest among differences at any two adjacent support points. Test statistic and confidence interval are constructed from a set of t-statistics based on double differences of the outcome variable, eliminating the need to estimate a conditional expectation function. Simulation evidence suggests that statistical power compares favorably to existing methods. We illustrate our approach by revisiting two studies from the economics of education literature.

Keywords: Regression discontinuity design; causal inference; policy evaluation; economics of education

JEL-codes: C12; C13; C14; I21

Language: English

48 pages, September 25, 2026

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