A version of this paper was presented at a seminar at the HighScope Perry Foundation, Ypsilanti, Michigan, December 2006, at a conference at the Minneapolis Federal Reserve in December 2007, at a conference on the role of early life conditions at the Michigan Poverty Research Center, University of Michigan, December 2007, at a Jacobs Foundation conference at Castle Marbach, April 2008, at the Leibniz Network Conference on Noncognitive Skills in Mannheim, Germany, May 2008, at an Institute for Research on Poverty conference, Madison, Wisconsin, June 2008, and at a conference on early childhood at the Brazilian National Academy of Sciences, Rio de Janeiro, Brazil, December 2009. We thank the editor and two anonymous referees for helpful comments which greatly improved this draft of the paper. We have benefited from comments received on early drafts of this paper at two brown bag lunches at the Statistics Department, University of Chicago, hosted by Stephen Stigler. We thank all of the workshop participants. In addition, we thank Amanda Agan, Mathilde Almlund, Joseph Altonji, Ricardo Barros, Dan Black, Steve Durlauf, Chris Hansman, Tim Kautz, Paul LaFontaine, Devesh Raval, Azeem Shaikh, Jeff Smith, and Steve Stigler for helpful comments. Our collaboration with Azeem Shaikh on related work has greatly strengthened the analysis in this paper. This research was supported in part by the American Bar Foundation, the Committee for Economic Development, by a grant from the Pew Charitable Trusts and the Partnership for America's Economic Success, the JB & MK Pritzker Family Foundation, Susan Thompson Buffett Foundation, Robert Dugger, and NICHD R01HD043411. The views expressed in this presentation are those of the authors and not necessarily those of the funders listed here. Supplementary materials for this paper are available online (Heckman, Moon, Pinto, Savelyev, and Yavitz (2010c)).
Analyzing social experiments as implemented: A reexamination of the evidence from the HighScope Perry Preschool Program
Article first published online: 3 AUG 2010
Copyright © 2010 James Heckman, Seong Hyeok Moon, Rodrigo Pinto, Peter Savelyev, and Adam Yavitz
Volume 1, Issue 1, pages 1–46, July 2010
How to Cite
Heckman, J., Moon, S. H., Pinto, R., Savelyev, P. and Yavitz, A. (2010), Analyzing social experiments as implemented: A reexamination of the evidence from the HighScope Perry Preschool Program. Quantitative Economics, 1: 1–46. doi: 10.3982/QE8
- Issue published online: 3 AUG 2010
- Article first published online: 3 AUG 2010
- Submitted August, 2009. Final version accepted May, 2010.
- Early childhood intervention;
- compromised randomization;
- social experiment;
- multiple-hypothesis testing
Social experiments are powerful sources of information about the effectiveness of interventions. In practice, initial randomization plans are almost always compromised. Multiple hypotheses are frequently tested. “Significant” effects are often reported with p-values that do not account for preliminary screening from a large candidate pool of possible effects. This paper develops tools for analyzing data from experiments as they are actually implemented.
We apply these tools to analyze the influential HighScope Perry Preschool Program. The Perry program was a social experiment that provided preschool education and home visits to disadvantaged children during their preschool years. It was evaluated by the method of random assignment. Both treatments and controls have been followed from age 3 through age 40.
Previous analyses of the Perry data assume that the planned randomization protocol was implemented. In fact, as in many social experiments, the intended randomization protocol was compromised. Accounting for compromised randomization, multiple-hypothesis testing, and small sample sizes, we find statistically significant and economically important program effects for both males and females. We also examine the representativeness of the Perry study.