Gli indici di effect size nella ricerca educativa. Analisi comparativa e significatività pratica

Effect sizes are statistical indexes used to quantify the difference between two groups, typically adopted in educational research to measure the efficacy of an intervention. Their use in research reports is recommended by the most important international research association in the field of psychology and education, such as the American Psychological Association (APA) and the American Educational Research Association (AERA). In this work, through a comparative analysis, after a brief description of the most widely used effect size indexes in educational research, authors provide practical indications about their use, and their interpretation. With this purpose in mind, a comparative analysis among Glass’ Δ, Cohen’s d and Hedeges’ g has been carried out, so that to observe their «behavior» in relation to different conditions of study design and to know which one is better to use in those conditions.