ABSTRACT
Statistical significance, effect size and statistical power carry great weight in quantitative educational research and this chapter addresses these three key factors. It explains what they are, what they mean and how to work with them. The chapter cautions against over-reliance on significance testing and indicates several concerns about null hypothesis significance testing (NHST). In addressing significance testing, and as an introduction to effect size, the chapter introduces correlational analysis, and advocates complementing significance testing with the use of effect size. It indicates different measures of effect size used with different statistics and how to calculate effect size, since measures of effect size, be they in terms of standardized units, original units or unit-free measures, vary according to the statistical tests used to calculate them. The chapter introduces statistical power, and, in doing so, clarifies Type I and Type II errors, what they mean and how to avoid them.
