It's the effect size, stupid: what effect size is and why it is important
It's the Effect Size, StupidWhat effect size is and why it is important Robert CoeSchool of Education, University of Durham, email firstname.lastname@example.org Paper presented at the Annual Conference of the British Educational Research Association, University of Exeter, England, 12-14 September 2002 Abstract Effect size is a simple way of quantifying the difference between two groups that has many advantages over the use of tests of statistical significance alone. 'Effect size' is simply a way of quantifying the size of the difference between two groups. The routine use of effect sizes, however, has generally been limited to meta-analysis - for combining and comparing estimates from different studies - and is all too rare in original reports of educational research (Keselman et al., 1998). The following guide is written for non-statisticians, though inevitably some equations and technical language have been used. 1. (a) (b) Figure 1 2. Equation 1 3. Table I: Interpretations of effect sizes 4. 5. 6. 7.