A Primer for Interpreting and Designing Difference-in-Differences Studies in Higher Education Research

Living reference work entry
Part of the Higher Education: Handbook of Theory and Research book series (HATR, volume 35)


Though randomized control trials continue to serve as the “gold standard” of causal inference, they are neither feasible nor desirable in numerous instances. Even in the absence of randomized trials, higher education researchers have at their disposal several statistical tools for estimating causal relationships. One such method is difference-in-differences, a powerful and intuitive approach to causal evaluation that exploits variation in the timing and coverage of policies. The method lends itself well to studying higher education policies and initiatives, as these frequently diffuse over time and across space in ways that may permit for causal inference. Difference-in-differences has become one of the most widely used methods for causal inference in higher education research. We use this chapter to introduce new researchers to this method with an overview of difference-in-differences models, common threats to their validity, and robustness checks. We then present extensions of the method, including event study models and variation in treatment timing. We illustrate these methods throughout the chapter by analyzing the effect of hurricanes on enrollment at affected colleges using data from the Integrated Postsecondary Education Data System and provide Stata code for replication of the analysis.


Policy evaluation Causal inference Quasi-experimental design Natural experiments Counterfactuals Difference-in-differences Event study models Parallel trends assumptions Fixed effects models Variation in treatment timing Heterogeneous effects Robustness checks Multiple comparison groups Clustered and bootstrapped standard errors Hurricane Katrina Geography of college choice Enrollment trends 


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Authors and Affiliations

  1. 1.Center for the Study of Higher and Postsecondary Education, School of EducationUniversity of MichiganAnn ArborUSA
  2. 2.University of Wisconsin-MadisonMadisonUSA

Section editors and affiliations

  • Laura W. Perna
    • 1
  • Ann Austin
    • 2
  • Linda Eisenmann
  • Pamela Eddy
    • 3
  • Adrianna Kezar
    • 4
  • Anne-Marie Nunez
  • Shouping Hu
  • Anna Neumann
    • 5
  • Nicholas A Bowman
  • Marvin Titus
  • Nicholas Hillman
    • 6
  1. 1.Graduate School of EducationUniversity of PennsylvaniaPhiladelphiaUSA
  2. 2.Michigan State UniversityEast LansingUSA
  3. 3.College of William and MaryWilliamsburgUSA
  4. 4.School of EducationUniversity of Southern CaliforniaLos AngelesUSA
  5. 5.Higher and Postsecondary EducationTeachers College, Columbia UniversityNew York CityUSA
  6. 6.University of WisconsinMadisonUSA

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