Discussion of AnneTheAgile's comment: Source: My summary of the Conclusion+Skim+My ideas.
Summary:
1.Motivates and describes the use of a metric for quantifying experimental results.
2.Effect size is normally a highly semantically meaningful measure of differences found in an experiment, so it should be included in all results, with preference over tests of statistical significance, which emphasize the sample size's significance.
3.Raw 'unstandardised' mean differences, together with a confidence interval, might be better than the Effect Size metricwhen a sample has restricted range or does not come from a Normal distribution, or if the measurement from which it was derived has unknown reliability.