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Conclusions beyond support: overconfident estimates in mixed models

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  • Holger Schielzeth
  • Wolfgang Forstmeier

Abstract

Mixed-effect models are frequently used to control for the nonindependence of data points, for example, when repeated measures from the same individuals are available. The aim of these models is often to estimate fixed effects and to test their significance. This is usually done by including random intercepts, that is, intercepts that are allowed to vary between individuals. The widespread belief is that this controls for all types of pseudoreplication within individuals. Here we show that this is not the case, if the aim is to estimate effects that vary within individuals and individuals differ in their response to these effects. In these cases, random intercept models give overconfident estimates leading to conclusions that are not supported by the data. By allowing individuals to differ in the slopes of their responses, it is possible to account for the nonindependence of data points that pseudoreplicate slope information. Such random slope models give appropriate standard errors and are easily implemented in standard statistical software. Because random slope models are not always used where they are essential, we suspect that many published findings have too narrow confidence intervals and a substantially inflated type I error rate. Besides reducing type I errors, random slope models have the potential to reduce residual variance by accounting for between-individual variation in slopes, which makes it easier to detect treatment effects that are applied between individuals, hence reducing type II errors as well. Copyright 2009, Oxford University Press.

Suggested Citation

  • Holger Schielzeth & Wolfgang Forstmeier, 2009. "Conclusions beyond support: overconfident estimates in mixed models," Behavioral Ecology, International Society for Behavioral Ecology, vol. 20(2), pages 416-420.
  • Handle: RePEc:oup:beheco:v:20:y:2009:i:2:p:416-420
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    File URL: http://hdl.handle.net/10.1093/beheco/arn145
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    Cited by:

    1. Stéphane Thériault & Marc-André Villard & Samuel Haché, 2012. "Habitat selection in site-faithful ovenbirds and recruits in the absence of experimental attraction," Behavioral Ecology, International Society for Behavioral Ecology, vol. 23(6), pages 1289-1295.
    2. Douglas J Krause & Jefferson T Hinke & Wayne L Perryman & Michael E Goebel & Donald J LeRoi, 2017. "An accurate and adaptable photogrammetric approach for estimating the mass and body condition of pinnipeds using an unmanned aerial system," PLOS ONE, Public Library of Science, vol. 12(11), pages 1-20, November.
    3. Reina, Christopher S. & Kudesia, Ravi S., 2020. "Wherever you go, there you become: How mindfulness arises in everyday situations," Organizational Behavior and Human Decision Processes, Elsevier, vol. 159(C), pages 78-96.
    4. Charline Couchoux & Jeanne Clermont & Dany Garant & Denis Réale & Jonathan PruittHandling editor, 2018. "Signaler and receiver boldness influence response to alarm calls in eastern chipmunks," Behavioral Ecology, International Society for Behavioral Ecology, vol. 29(1), pages 212-220.
    5. Lars Kulik & Doreen Langos & Anja Widdig, 2016. "Mothers Make a Difference: Mothers Develop Weaker Bonds with Immature Sons than Daughters," PLOS ONE, Public Library of Science, vol. 11(5), pages 1-14, May.
    6. Andrés López-Sepulcre & Sebastiano De Bona & Janne K. Valkonen & Kate D.L. Umbers & Johanna Mappes, 2015. "Item Response Trees: a recommended method for analyzing categorical data in behavioral studies," Behavioral Ecology, International Society for Behavioral Ecology, vol. 26(5), pages 1268-1273.
    7. Pasquali, Giovanni & Krishnan, Aarti & Alford, Matthew, 2021. "Multichain strategies and economic upgrading in global value chains: Evidence from Kenyan horticulture," World Development, Elsevier, vol. 146(C).
    8. Caleb R. Hickman & James I. Watling, 2014. "Leachates from an invasive shrub causes risk-prone behavior in a larval amphibian," Behavioral Ecology, International Society for Behavioral Ecology, vol. 25(2), pages 300-305.
    9. Laura A. B. Wilson & Susanne R. K. Zajitschek & Malgorzata Lagisz & Jeremy Mason & Hamed Haselimashhadi & Shinichi Nakagawa, 2022. "Sex differences in allometry for phenotypic traits in mice indicate that females are not scaled males," Nature Communications, Nature, vol. 13(1), pages 1-12, December.
    10. Paula Hidalgo-Rodríguez & Pedro Sáez-Gómez & Julio Blas & Anders Hedenström & Carlos Camacho, 2021. "Body mass dynamics of migratory nightjars are explained by individual turnover and fueling," Behavioral Ecology, International Society for Behavioral Ecology, vol. 32(6), pages 1086-1093.

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