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ERIC Number: EJ1020332
Record Type: Journal
Publication Date: 2014-Apr
Pages: 20
Abstractor: As Provided
Reference Count: 13
ISBN: N/A
ISSN: ISSN-1076-9986
Measuring an Effect Size from Dichotomized Data: Contrasted Results Whether Using a Correlation or an Odds Ratio
Rousson, Valentin
Journal of Educational and Behavioral Statistics, v39 n2 p144-163 Apr 2014
It is well known that dichotomizing continuous data has the effect to decrease statistical power when the goal is to test for a statistical association between two variables. Modern researchers however are focusing not only on statistical significance but also on an estimation of the "effect size" (i.e., the strength of association between the variables) to judge whether a significant association is also clinically relevant. In this article, we are interested in the consequences of dichotomizing continuous data on the value of an effect size in some classical settings. It turns out that the conclusions will not be the same whether using a correlation or an odds ratio to summarize the strength of association between the variables: Whereas the value of a correlation is typically decreased by a factor [square root of pi/2] after each dichotomization, the value of an odds ratio is at the same time raised to the power [square root of 2]. From a descriptive statistical point of view, it is thus not clear whether dichotomizing continuous data leads to a decrease or to an increase in the effect size, as illustrated using a data set to investigate the relationship between motor and intellectual functions in children and adolescents.
SAGE Publications. 2455 Teller Road, Thousand Oaks, CA 91320. Tel: 800-818-7243; Tel: 805-499-9774; Fax: 800-583-2665; e-mail: journals@sagepub.com; Web site: http://sagepub.com
Publication Type: Journal Articles; Reports - Evaluative
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A