Abstract
The purpose of this study is to find less biased effect size index in one-way analysis of variance (ANOVA) by performing a thorough Monte Carlo study with 1,000,000 replications per condition. Our results show that contrary to common belief, epsilon squared is the least biased among the threemajorindices, while omega squared produces the least root mean squared errors, for all conditions. Although eta squared results in the least standard deviation, this does not necessarily make it a good estimator because a considerable amount of bias still occurs when the sample size is small.
