ASSOCIATION FOR CONSUMER RESEARCH Labovitz School of Business & Economics, University of Minnesota Duluth, 11 E. Superior Street, Suite 210, Duluth, MN 55802 A Study of Effect Sizes in Marketing Experiments Roger Marshall, Nanyang University Loi Soh Loi, Nanyang University Na WoonBong, Kyunghee University ABSTRACT - An investigation is undertaken to empirically document the reported effect sizes of experiments reported in four leading marketing journals from the period 1985 to 1995, following a previous study concerned with the prior decade (Peterson, Albaum & Beltramini, 1985). Using omega-squared (w2), Pearson's coefficient (r) and Cohen's index (d) as measures of effect size, the results of 269 experiments, yielding a total of 1,399 experimental effects, were analyzed for the proportion of variance explained. Average incidence of reported w2 values has increased from 14% to 25% of experiments since the prior decade, but are still somewhat low. [to cite]: Roger Marshall, Loi Soh Loi, and Na WoonBong (2004) ,"A Study of Effect Sizes in Marketing Experiments", in NA - Advances in Consumer Research Volume 31, eds. Barbara E. Kahn and Mary Frances Luce, Valdosta, GA : Association for Consumer Research, Pages: 514-520. [url]: http://www.acrwebsite.org/volumes/8953/volumes/v31/NA-31 [copyright notice]: This work is copyrighted by The Association for Consumer Research. For permission to copy or use this work in whole or in part, please contact the Copyright Clearance Center at http://www.copyright.com/.