Selection Bias in Web Surveys and the Use of Propensity Scores

Published in: Sociological Methods and Research, v. 37, no. 3, Feb. 2009, p. 291-318

Posted on RAND.org on January 01, 2009

by Matthias Schonlau, Arthur van Soest, Arie Kapteyn, Mick Couper

Read More

Access further information on this document at Sociological Methods and Research

This article was published outside of RAND. The full text of the article can be found at the link above.

Web surveys are a popular survey mode, but the subpopulation with Internet access may not represent the population of interest. The authors investigate whether adjusting using weights or matching on a small set of variables makes the distributions of target variables representative of the population. This application has a rich sampling design; the Internet sample is part of an existing probability sample, the Health and Retirement Study, that is representative of the U.S. population aged 50 and older. For the dichotomous variables investigated, the adjustment helps. On average, the sample means in the Internet access sample differ by 6.5 percent before and 3.7 percent after adjustment. Still, a large number of adjusted estimates remain significantly different from their target estimates based on the complete sample. This casts doubt on the common procedure to use only a few variables to correct for the selectivity of convenience samples.

This report is part of the RAND Corporation External publication series. Many RAND studies are published in peer-reviewed scholarly journals, as chapters in commercial books, or as documents published by other organizations.

Our mission to help improve policy and decisionmaking through research and analysis is enabled through our core values of quality and objectivity and our unwavering commitment to the highest level of integrity and ethical behavior. To help ensure our research and analysis are rigorous, objective, and nonpartisan, we subject our research publications to a robust and exacting quality-assurance process; avoid both the appearance and reality of financial and other conflicts of interest through staff training, project screening, and a policy of mandatory disclosure; and pursue transparency in our research engagements through our commitment to the open publication of our research findings and recommendations, disclosure of the source of funding of published research, and policies to ensure intellectual independence. For more information, visit www.rand.org/about/principles.

The RAND Corporation is a nonprofit institution that helps improve policy and decisionmaking through research and analysis. RAND's publications do not necessarily reflect the opinions of its research clients and sponsors.