IDEAS home Printed from
MyIDEAS: Login to save this article or follow this journal

Inference with "Difference in Differences" with a Small Number of Policy Changes

  • Timothy G. Conley

    (Booth School of Business, University of Chicago)

  • Christopher R. Taber

    (University of Wisconsin-–Madison)

In difference-in-differences applications, identification of the key parameter often arises from changes in policy by a small number of groups. In contrast, typical inference assumes that the number of groups changing policy is large. We present an alternative inference approach for a small (finite) number of policy changers, using information from a large sample of nonchanging groups. Treatment effect point estimators are not consistent, but we can consistently estimate their asymptotic distribution under any point null hypothesis about the treatment. Thus, treatment point estimators can be used as test statistics, and confidence intervals can be constructed using test statistic inversion. © 2011 The President and Fellows of Harvard College and the Massachusetts Institute of Technology.

If you experience problems downloading a file, check if you have the proper application to view it first. In case of further problems read the IDEAS help page. Note that these files are not on the IDEAS site. Please be patient as the files may be large.

File URL:
File Function: link to full text
Download Restriction: Access to full text is restricted to subscribers.

As the access to this document is restricted, you may want to look for a different version under "Related research" (further below) or search for a different version of it.

Article provided by MIT Press in its journal The Review of Economics and Statistics.

Volume (Year): 93 (2011)
Issue (Month): 1 (February)
Pages: 113-125

in new window

Handle: RePEc:tpr:restat:v:93:y:2011:i:1:p:113-125
Contact details of provider: Web page:

Order Information: Web:

References listed on IDEAS
Please report citation or reference errors to , or , if you are the registered author of the cited work, log in to your RePEc Author Service profile, click on "citations" and make appropriate adjustments.:

as in new window
  1. Bruce D. Meyer, 1994. "Natural and Quasi- Experiments in Economics," NBER Technical Working Papers 0170, National Bureau of Economic Research, Inc.
  2. David Card, 1990. "The impact of the Mariel boatlift on the Miami labor market," Industrial and Labor Relations Review, ILR Review, Cornell University, ILR School, vol. 43(2), pages 245-257, January.
  3. Susan Athey & Guido W. Imbens, 2002. "Identification and Inference in Nonlinear Difference-In-Differences Models," NBER Technical Working Papers 0280, National Bureau of Economic Research, Inc.
  4. Anderson, Patricia M. & Meyer, Bruce D., 2000. "The effects of the unemployment insurance payroll tax on wages, employment, claims and denials," Journal of Public Economics, Elsevier, vol. 78(1-2), pages 81-106, October.
  5. Card, David & Krueger, Alan B, 1994. "Minimum Wages and Employment: A Case Study of the Fast-Food Industry in New Jersey and Pennsylvania," American Economic Review, American Economic Association, vol. 84(4), pages 772-93, September.
  6. Gary T. Henry & Ross Rubenstein, 2002. "Paying for grades: Impact of merit-based financial aid on educational quality," Journal of Policy Analysis and Management, John Wiley & Sons, Ltd., vol. 21(1), pages 93-109.
  7. Chamberlain, Gary, 1980. "Analysis of Covariance with Qualitative Data," Review of Economic Studies, Wiley Blackwell, vol. 47(1), pages 225-38, January.
  8. Susan Dynarski, 2004. "The New Merit Aid," NBER Chapters, in: College Choices: The Economics of Where to Go, When to Go, and How to Pay For It, pages 63-100 National Bureau of Economic Research, Inc.
  9. Matzkin, Rosa L., 1986. "Restrictions of economic theory in nonparametric methods," Handbook of Econometrics, in: R. F. Engle & D. McFadden (ed.), Handbook of Econometrics, edition 1, volume 4, chapter 42, pages 2523-2558 Elsevier.
  10. Gallant, A Ronald & Nychka, Douglas W, 1987. "Semi-nonparametric Maximum Likelihood Estimation," Econometrica, Econometric Society, vol. 55(2), pages 363-90, March.
  11. Moulton, Brent R, 1990. "An Illustration of a Pitfall in Estimating the Effects of Aggregate Variables on Micro Unit," The Review of Economics and Statistics, MIT Press, vol. 72(2), pages 334-38, May.
  12. Angrist, Joshua D. & Krueger, Alan B., 1999. "Empirical strategies in labor economics," Handbook of Labor Economics, in: O. Ashenfelter & D. Card (ed.), Handbook of Labor Economics, edition 1, volume 3, chapter 23, pages 1277-1366 Elsevier.
  13. Stephen G. Donald & Kevin Lang, 2007. "Inference with Difference-in-Differences and Other Panel Data," The Review of Economics and Statistics, MIT Press, vol. 89(2), pages 221-233, May.
  14. repec:tpr:qjecon:v:119:y:2004:i:1:p:249-275 is not listed on IDEAS
  15. Christopher M. Cornwell & David B. Mustard & Deepa Sridhar, 2005. "The Enrollment Effects of Merit-Based Financial Aid: Evidence from Georgia's HOPE Scholarship," HEW 0501002, EconWPA.
  16. Marianne Bertrand & Esther Duflo & Sendhil Mullainathan, 2002. "How Much Should We Trust Differences-in-Differences Estimates?," NBER Working Papers 8841, National Bureau of Economic Research, Inc.
  17. Susan Dynarski, 2000. "Hope for Whom? Financial Aid for the Middle Class and Its Impact on College Attendance," NBER Working Papers 7756, National Bureau of Economic Research, Inc.
  18. Newey, Whitney K. & McFadden, Daniel, 1986. "Large sample estimation and hypothesis testing," Handbook of Econometrics, in: R. F. Engle & D. McFadden (ed.), Handbook of Econometrics, edition 1, volume 4, chapter 36, pages 2111-2245 Elsevier.
  19. Dynarski, Susan, 2000. "Hope for Whom? Financial Aid for the Middle Class and Its Impact on College Attendance," National Tax Journal, National Tax Association, vol. 53(n. 3), pages 629-62, September.
Full references (including those not matched with items on IDEAS)

This item is not listed on Wikipedia, on a reading list or among the top items on IDEAS.

When requesting a correction, please mention this item's handle: RePEc:tpr:restat:v:93:y:2011:i:1:p:113-125. See general information about how to correct material in RePEc.

For technical questions regarding this item, or to correct its authors, title, abstract, bibliographic or download information, contact: (Anna Pollock-Nelson)

If you have authored this item and are not yet registered with RePEc, we encourage you to do it here. This allows to link your profile to this item. It also allows you to accept potential citations to this item that we are uncertain about.

If references are entirely missing, you can add them using this form.

If the full references list an item that is present in RePEc, but the system did not link to it, you can help with this form.

If you know of missing items citing this one, you can help us creating those links by adding the relevant references in the same way as above, for each refering item. If you are a registered author of this item, you may also want to check the "citations" tab in your profile, as there may be some citations waiting for confirmation.

Please note that corrections may take a couple of weeks to filter through the various RePEc services.

This information is provided to you by IDEAS at the Research Division of the Federal Reserve Bank of St. Louis using RePEc data.