Standardized or simple effect size: What should be reported?
2008/11/17 by Thom Baguley · 635 citations
Computer Science · Decision Sciences · Mathematics · Psychology · #Advanced Statistical Modeling Techniques #Confidence interval #Context (archaeology) #Mathematics #Meta-analysis and systematic reviews #Metric (unit) #Point (geometry) #Preference #Psychology #Psychometric Methodologies and Testing #Sample size determination #Simple (philosophy) #Statistic #Statistics #Strictly standardized mean difference
paper · doi:10.1348/000712608x377117
published in British Journal of Psychology 100(3), 603-617 (Wiley)
openalex publication_date 2008/11/17 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/31
Abstract
It is regarded as best practice for psychologists to report effect size when disseminating quantitative research findings. Reporting of effect size in the psychological literature is patchy - though this may be changing - and when reported it is far from clear that appropriate effect size statistics are employed. This paper considers the practice of reporting point estimates of standardized effect size and explores factors such as reliability, range restriction and differences in design that distort standardized effect size unless suitable corrections are employed. For most purposes simple (unstandardized) effect size is more robust and versatile than standardized effect size. Guidelines for deciding what effect size metric to use and how to report it are outlined. Foremost among these are: (i) a preference for simple effect size over standardized effect size, and (ii) the use of confidence intervals to indicate a plausible range of values the effect might take. Deciding on the appropriate effect size statistic to report always requires careful thought and should be influenced by the goals of the researcher, the context of the research and the potential needs of readers.
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