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When small effect sizes become huge: Synaesthesia is linked to very large differences in cognition
1University of Sussex, UK.
Perception
|December 6, 2023
Summary
The replication crisis in psychology often leads to expectations of small effects. However, multivariate effect sizes like Mahalanobis D reveal substantial group differences from multiple small effects, offering a more complete picture.
Area of Science:
- Psychology
- Statistics
Background:
- The replication crisis in psychology has led to an expectation of small-to-medium effect sizes in psychological research.
- Current effect size calculations typically focus on single variables, potentially underestimating true group differences.
Purpose of the Study:
- To investigate the utility of multivariate effect sizes in revealing larger group differences.
- To reanalyze existing multivariate datasets using Mahalanobis D.
Main Methods:
- Reanalyzed multivariate datasets from studies comparing synaesthetes and controls.
- Employed Mahalanobis D, the multivariate extension of Cohen's d, to assess group differences.
Main Results:
- Mahalanobis D demonstrated that a collection of small-to-medium effects across multiple variables can result in very large overall group differences.
- This approach highlights potentially underappreciated psychological distinctions between groups.
Conclusions:
- Multivariate effect sizes provide a more comprehensive measure of psychological differences than univariate approaches.
- The underestimation of effect sizes in psychological research may be mitigated by adopting multivariate statistical methods.
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