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

Marta Pellegrini, Giuliano Vivanet, Roberto Trinchero


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.


Educational efficacy evaluation; Effect size; Evidence informed education; Experimental studies; Practical significance.

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DOI: https://doi.org/10.7358/ecps-2018-018-pel1


Journal of Educational, Cultural and Psychological Studies (ECPS)
Registered by Tribunale di Milano (19/05/2010 n. 278)
Online ISSN 2037-7924 - Print ISSN 2037-7932

Research Laboratory on Didactics and Evaluation - Department of Education - "Roma Tre" University

Executive Editor: Gaetano Domenici - Managing  Editor: Valeria Biasci
Editorial Board: Giuditta Alessandrini - Eleftheria Argyropoulou - Massimo Baldacci - Joao Barroso - Richard Bates - Christofer Bezzina - Paolo Bonaiuto - Lucia Boncori - Pietro Boscolo - Sara Bubb  - Carlo Felice Casula - Jean-Émile Charlier - Lucia Chiappetta Cajola - Carmela Covato - Jean-Louis Derouet - Peter Early - Franco Frabboni - Constance Katz - James Levin - Pietro Lucisano  - Roberto Maragliano - Romuald Normand - Michael Osborne - Donatella Palomba - Michele Pellerey - Clotilde Pontecorvo - Vitaly V. Rubtzov - Jaap Scheerens - Noah W. Sobe - Francesco Susi - Giuseppe Spadafora - Pat Thomson
Editorial Staff: Fabio Alivernini - Guido Benvenuto - Anna Maria Ciraci - Massimiliano Fiorucci - Luca Mallia - Massimo Margottini - Giovanni Moretti - Carla Roverselli 
Editorial Secretary:
Nazarena Patrizi