D. STEPHEN voss is a doctoral candidate in the Department of Government of Harvard University. ANDREW GELMAN is assistant professor in the Department of Statistics in the University of California, Berkeley. GARY KING is professor in the Department of Government of Harvard University. They thank the following individuals for their openness and detailed assistance: David K. Krane and Robert Spanski of Louis Harris and Associates; Martin Frankel, a consultant for Louis Harris and statistian at Baruch College; Kathleen Frankovic, Bala Ramnath, and Marla Kaye of CBS; Sharon Warden of the Washington Post; Kristen Conrad of Chilton Research; Dale Kulp and Amy Starer of Marketing Systems Group, responsible for the GENESYS Sampling System; Steve Shaw of Media General; Kathy Walenczyk and Linda Piekarski of Survey Sampling, Inc.; Dan Soulas of ICR Survey Research Group; Bums W. Roper, Peter Case, and Brad Fay of the Roper Organization; Hal Quinley of Yankelovich; Jeff Alderman of ABC; Shari Weber of Gallup; and especially Gallup's Jack Ludwig, who weathered the inherent inefficiency of a trial run. They also thank Mark Lew and Cassie Hartzog for programming assistance; Bradley Palmquist, Dale Kulp, Roger Purves, Bob Groves, and anonymous reviewers for comments and corrections; and the National Science Foundation for grants SBR-9223637 (to Gelman and King), DMS-9457824 (to Gelman), and SBR-932121 (to King). Gary King also thanks the John Simon Guggenheim Memorial Foundation for a fellowship during which time this research was completed. E-mail addresses are Voss, dsvoss@isr.harvard.edu; Gelman, gelman@stat.berkeley.edu; King, gking@harvard.edu. 1. Most of these data are available through the Inter-University Consortium for Political and Social Research (ICPSR) or the Roper Center for Public Opinion Research.