title: Basics of meta-analysis: I2is not an absolute measure of heterogeneity.
abstract: When we speak about heterogeneity in a meta-analysis, our intent is usually to understand the substantive implications of the heterogeneity. If an intervention yields a mean effect size of 50 points, we want to know if the effect size in different populations varies from 40 to 60, or from 10 to 90, because this speaks to the potential utility of the intervention. While there is a common belief that the I2statistic provides this information, it actually does not. In this example, if we are told that I2is 50%, we have no way of knowing if the effects range from 40 to 60, or from 10 to 90, or across some other range. Rather, if we want to communicate the predicted range of effects, then we should simply report this range. This gives readers the information they think is being captured by I2and does so in a way that is concise and unambiguous. Copyright © 2017 John Wiley & Sons, Ltd.
authors.affiliation: BioStat, Inc., Englewood, NJ, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Borenstein
authors.affiliation: School of Social and Community Medicine, University of Bristol, Bristol, UK.
authors.forename: Julian P T
authors.initials: JP
authors.lastname: Higgins
authors.affiliation: Department of Statistics, Northwestern University, Evanston, IL, USA.
authors.forename: Larry V
authors.initials: LV
authors.lastname: Hedges
authors.affiliation: Department of Management, Baruch College-City University of New York, New York, NY, USA.
authors.forename: Hannah R
authors.initials: HR
authors.lastname: Rothstein
mesh_terms: D000465:Algorithms; D001289:Attention Deficit Disorder with Hyperactivity / Q000188:drug therapy; D001290:Attitude; D003071:Cognition / Q000187:drug effects; D015987:Effect Modifier, Epidemiologic; D007172:Erectile Dysfunction / Q000188:drug therapy; D005260:Female; D006801:Humans; D008297:Male; D015201:Meta-Analysis as Topic; D008774:Methylphenidate / Q000627:therapeutic use; D015233:Models, Statistical; D009035:Mothers; D015995:Prevalence; D015203:Reproducibility of Results; D012107:Research Design; D013223:Statistics as Topic; D013313:Stress Disorders, Post-Traumatic / Q000628:therapy; D016896:Treatment Outcome
chemical_list: D008774:Methylphenidate
keywords: I-squared; I2; heterogeneity; inconsistency; meta-analysis; prediction intervals