Cohen's d Statistic
Shayne B. Piasta & Laura M. Justice
Cohen's d statistic is a type of effect size . An effect size is a specific numerical nonzero value used to represent the extent to which a null hypothesis is false. As an effect size, Cohen's d is typically used to represent the magnitude of differences between two (or more) groups on a given variable, with larger values representing a greater differentiation between the two groups on that variable. When comparing means in a scientific study, the reporting of an effect size such as Cohen's d is considered complementary to the reporting of results from a test of statistical significance. Whereas the test of statistical significance is used to suggest whether a null hypothesis is true (no difference exists between Populations A and B for a specific phenomenon) or false (a difference exists between Populations A and B for a specific phenomenon), the calculation of an effect size estimate is ...