Wednesday, August 11, 2010

Analysing Social Experiments - Heckman

Analyzing Social Experiments as Implemented: A Reexamination of the Evidence From the HighScope Perry Preschool Program

Author info | Abstract | Publisher info | Download info | Related research | Statistics
Author Info
James J. Heckman (University of Chicago, University College Dublin, Yale University and the American Bar Foundation)
Seong Hyeok Moon (Department of Economics, University of Chicago)
Rodrigo Pinto (Department of Economics, University of Chicago)
Peter A. Savelyev (Department of Economics, University of Chicago)
Adam Yavitz (Economic Research Center, University of Chicago)

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. "Signicant" 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.

1 comment:

Mark McG said...

The “representativeness” issue and the extent to which you can generalise from these interventions has always troubled me, especially in light of the recent papers (including some by Prof. Heckman) which are skeptical of drawing inference from local average treatment effects derived from instrumental variable estimators. After all, Perry took place in a disadvantaged, African American community in 1960s Michigan.

Having said that, a comparison with NLSY79 provided in this paper seems to suggest that the Perry sample was reasonably representative of disadvantaged African Americans.