Hedges Larry V
Northwestern University, Evanston, IL, USA.
Educ Psychol Meas. 2024 Oct 6:00131644241278928. doi: 10.1177/00131644241278928.
The standardized mean difference (sometimes called Cohen's d) is an effect size measure widely used to describe the outcomes of experiments. It is mathematically natural to describe differences between groups of data that are normally distributed with different means but the same standard deviation. In that context, it can be interpreted as determining several indexes of overlap between the two distributions. If the data are not approximately normally distributed or if they have substantially unequal standard deviations, the relation between d and overlap between distributions can be very different, and interpretations of d that apply when the data are normal with equal variances are unreliable.
标准化均数差（有时称为科恩d值）是一种效应量度，广泛用于描述实验结果。对于均值不同但标准差相同的正态分布数据集之间的差异，从数学角度自然可以进行描述。在这种情况下，它可以解释为确定两种分布之间的几个重叠指数。如果数据不是近似正态分布，或者它们的标准差存在很大差异，那么d值与分布重叠之间的关系可能会非常不同，并且在数据呈正态分布且方差相等时适用的d值解释是不可靠的。
