Baseline, Placebo, and Treatment: Efficient Estimation for Three-Group Experiments

Political Analysis, Vol. 18, No. 3, pp. 297-315, 2010

Posted: 5 Jan 2011

See all articles by Alan Gerber

Alan Gerber

Yale University - Department of Political Science; Yale University - Cowles Foundation

Donald P. Green

Columbia University

Edward H. Kaplan

Yale School of Management

Holger L. Kern

Florida State University - Department of Political Science

Date Written: May 1, 2010

Abstract

Randomized experiments commonly compare subjects receiving a treatment to subjects receiving a placebo. An alternative design, frequently used in field experimentation, compares subjects assigned to an untreated baseline group to subjects assigned to a treatment group, adjusting statistically for the fact that some members of the treatment group may fail to receive the treatment. This article shows the potential advantages of a three-group design (baseline, placebo, and treatment). We present a maximum likelihood estimator of the treatment effect for this three-group design and illustrate its use with a field experiment that gauges the effect of prerecorded phone calls on voter turnout. The three-group design offers efficiency advantages over two-group designs while at the same time guarding against unanticipated placebo effects (which would undermine the placebo-treatment comparison) and unexpectedly low rates of compliance with the treatment assignment (which would undermine the baseline-treatment comparison).

Keywords: Field Experiment, Three-Group Design, Voter Turnout

JEL Classification: C93, C00

Suggested Citation

Gerber, Alan and Green, Donald P. and Kaplan, Edward H. and Kern, Holger L., Baseline, Placebo, and Treatment: Efficient Estimation for Three-Group Experiments (May 1, 2010). Political Analysis, Vol. 18, No. 3, pp. 297-315, 2010 , Available at SSRN: https://ssrn.com/abstract=1734787

Alan Gerber

Yale University - Department of Political Science ( email )

Box 208269
New Haven, DC 06520-8269
United States
203-432-5232 (Phone)

Yale University - Cowles Foundation

Box 208281
New Haven, CT 06520-8281
United States

Donald P. Green (Contact Author)

Columbia University ( email )

7th Floor, International Affairs Bldg.
420 W. 118th Street
New York, NY 10027
United States

Edward H. Kaplan

Yale School of Management ( email )

135 Prospect Street
P.O. Box 208200
New Haven, CT 06520-8200
United States
203-432-6031 (Phone)

Holger L. Kern

Florida State University - Department of Political Science ( email )

Tallahassee, FL 30306
United States

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