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The Effects of Nonnormal Distributions on Confidence Intervals Around the Standardized Mean Difference: Bootstrap and Parametric Confidence IntervalsUniversity of Notre Dame, kkelley{at}nd.edu
The standardized group mean difference, Cohen’s d, is among the most commonly used and intuitively appealing effect sizes for group comparisons. However, reporting this point estimate alone does not reflect the extent to which sampling error may have led to an obtained value. A confidence interval expresses the uncertainty that exists between d and the population value,
Key Words: effect size • standardized effect size • confidence intervals • bootstrap methods • nonnormal data
Educational and Psychological Measurement, Vol. 65, No. 1,
51-69 (2005) This article has been cited by other articles:
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, it represents. A set of Monte Carlo simulations was conducted to examine the integrity of a noncentral approach analogous to that given by Steiger and Fouladi, as well as two bootstrap approaches in situations in which the normality assumption is violated. Because d is positively biased, a procedure given by Hedges and Olkin is outlined, such that an unbiased estimate of 
