Nonparametric Tests for Treatment Effect Heterogeneity

Richard K. Crump, V. Joseph Hotz, Guido W. Imbens, Oscar A. Mitnik

NBER Technical Working Paper No. 324
Issued in June 2006
NBER Program(s):   TWP

A large part of the recent literature on program evaluation has focused on estimation of the average effect of the treatment under assumptions of unconfoundedness or ignorability following the seminal work by Rubin (1974) and Rosenbaum and Rubin (1983). In many cases however, researchers are interested in the effects of programs beyond estimates of the overall average or the average for the subpopulation of treated individuals. It may be of substantive interest to investigate whether there is any subpopulation for which a program or treatment has a nonzero average effect, or whether there is heterogeneity in the effect of the treatment. The hypothesis that the average effect of the treatment is zero for all subpopulations is also important for researchers interested in assessing assumptions concerning the selection mechanism. In this paper we develop two nonparametric tests. The first test is for the null hypothesis that the treatment has a zero average effect for any subpopulation defined by covariates. The second test is for the null hypothesis that the average effect conditional on the covariates is identical for all subpopulations, in other words, that there is no heterogeneity in average treatment effects by covariates. Sacrificing some generality by focusing on these two specific null hypotheses we derive tests that are straightforward to implement.

download in pdf format
   (450 K)

email paper

Machine-readable bibliographic record - MARC, RIS, BibTeX

Document Object Identifier (DOI): 10.3386/t0324

Users who downloaded this paper also downloaded these:
Athey and Imbens t0280 Identification and Inference in Nonlinear Difference-In-Differences Models
Crump, Hotz, Imbens, and Mitnik t0330 Moving the Goalposts: Addressing Limited Overlap in the Estimation of Average Treatment Effects by Changing the Estimand
Angrist w9708 Treatment Effect Heterogeneity in Theory and Practice
Abadie and Imbens w15301 Matching on the Estimated Propensity Score
Imbens and Wooldridge w14251 Recent Developments in the Econometrics of Program Evaluation
NBER Videos

National Bureau of Economic Research, 1050 Massachusetts Ave., Cambridge, MA 02138; 617-868-3900; email:

Contact Us