Skip to ContentGo to accessibility pageKeyboard shortcuts menu
OpenStax Logo
Introductory Business Statistics

10.2 Cohen's Standards for Small, Medium, and Large Effect Sizes

Introductory Business Statistics10.2 Cohen's Standards for Small, Medium, and Large Effect Sizes

Cohen's d is a measure of "effect size" based on the differences between two means. Cohen’s d, named for United States statistician Jacob Cohen, measures the relative strength of the differences between the means of two populations based on sample data. The calculated value of effect size is then compared to Cohen’s standards of small, medium, and large effect sizes.

Size of effect d
Small 0.2
Medium 0.5
Large 0.8
Table 10.2 Cohen's Standard Effect Sizes

Cohen's d is the measure of the difference between two means divided by the pooled standard deviation: d= x ¯ 1 – x ¯ 2 s pooled d= x ¯ 1 – x ¯ 2 s pooled where s pooled = ( n 1 –1) s 1 2 +( n 2 –1) s 2 2 n 1 + n 2 –2 s pooled = ( n 1 –1) s 1 2 +( n 2 –1) s 2 2 n 1 + n 2 –2

It is important to note that Cohen's d does not provide a level of confidence as to the magnitude of the size of the effect comparable to the other tests of hypothesis we have studied. The sizes of the effects are simply indicative.

Example 10.4

Problem

Calculate Cohen’s d for example 10.2. Is the size of the effect small, medium, or large? Explain what the size of the effect means for this problem.

PreviousNext
Order a print copy
Citation/Attribution

This book may not be used in the training of large language models or otherwise be ingested into large language models or generative AI offerings without OpenStax's permission.

Want to cite, share, or modify this book? This book uses the Creative Commons Attribution License and you must attribute OpenStax.

Attribution information
  • If you are redistributing all or part of this book in a print format, then you must include on every physical page the following attribution:
    Access for free at https://openstax.org/books/introductory-business-statistics/pages/1-introduction
  • If you are redistributing all or part of this book in a digital format, then you must include on every digital page view the following attribution:
    Access for free at https://openstax.org/books/introductory-business-statistics/pages/1-introduction
Citation information

© Jun 23, 2022 OpenStax. Textbook content produced by OpenStax is licensed under a Creative Commons Attribution License . The OpenStax name, OpenStax logo, OpenStax book covers, OpenStax CNX name, and OpenStax CNX logo are not subject to the Creative Commons license and may not be reproduced without the prior and express written consent of Rice University.