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The Importance of Random Slopes in Mixed Models for Bayesian Hypothesis Testing


Oberauer, Klaus (2022). The Importance of Random Slopes in Mixed Models for Bayesian Hypothesis Testing. Psychological Science, 33(4):648-665.

Abstract

Mixed models are gaining popularity in psychology. For frequentist mixed models, previous research showed that excluding random slopes-differences between individuals in the direction and size of an effect-from a model when they are in the data can lead to a substantial increase in false-positive conclusions in null-hypothesis tests. Here, I demonstrated through five simulations that the same is true for Bayesian hypothesis testing with mixed models, which often yield Bayes factors reflecting very strong evidence for a mean effect on the population level even if there was no such effect. Including random slopes in the model largely eliminates the risk of strong false positives but reduces the chance of obtaining strong evidence for true effects. I recommend starting analysis by testing the support for random slopes in the data and removing them from the models only if there is clear evidence against them.

Abstract

Mixed models are gaining popularity in psychology. For frequentist mixed models, previous research showed that excluding random slopes-differences between individuals in the direction and size of an effect-from a model when they are in the data can lead to a substantial increase in false-positive conclusions in null-hypothesis tests. Here, I demonstrated through five simulations that the same is true for Bayesian hypothesis testing with mixed models, which often yield Bayes factors reflecting very strong evidence for a mean effect on the population level even if there was no such effect. Including random slopes in the model largely eliminates the risk of strong false positives but reduces the chance of obtaining strong evidence for true effects. I recommend starting analysis by testing the support for random slopes in the data and removing them from the models only if there is clear evidence against them.

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Additional indexing

Item Type:Journal Article, refereed, original work
Communities & Collections:06 Faculty of Arts > Institute of Psychology
Dewey Decimal Classification:150 Psychology
Scopus Subject Areas:Social Sciences & Humanities > General Psychology
Language:English
Date:April 2022
Deposited On:09 Aug 2022 09:39
Last Modified:29 Jan 2024 02:42
Publisher:Sage Publications
ISSN:0956-7976
OA Status:Hybrid
Publisher DOI:https://doi.org/10.1177/09567976211046884
PubMed ID:35357978
  • Content: Published Version
  • Language: English
  • Licence: Creative Commons: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)