Tatjana von Rosen: What effect size is and why/how to use it

Effect size is considered to be a simple way of quantifying the difference between two groups that has many advantages over the use of typical tests of statistical significance alone (e.g. t-test). It is easy to calculate and understand, and it is widely used, for example in educational research. I shall give a brief overview on what effect size is and when/how to use it.