How should we interpret estimates of individual repeatability?
© 2018 The Author(s). Evolution Letters published by Wiley Periodicals, Inc. on behalf of Society for the Study of Evolution (SSE) and European Society for Evolutionary Biology (ESEB). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
Individual repeatability (R), defined as the proportion of observed variance attributable to among-individual differences, is a widely used summary statistic in evolutionarily motivated studies of behaviour and (increasingly) physiology. Although statistical methods to estimate R are well known and widely available, there is a growing tendency for researchers to interpret R in ways that are subtly, but importantly, different. Some view R as a property of a data set and a statistic to be interpreted agnostically with respect to mechanism. Others wish to isolate the contributions of “intrinsic” and/or “permanent” individual differences, and draw a distinction between true (intrinsic) and pseudo-repeatability arising from uncontrolled extrinsic effects. This latter view proposes a narrower, more mechanistic interpretation, than the traditional concept of repeatability, but perhaps one that allows stronger evolutionary inference as a consequence (provided analytical pitfalls are successfully avoided). Neither perspective is incorrect, but if we are to avoid confusion and fruitless debate, there is a need for researchers to recognise this dichotomy, and to ensure clarity in relation to how, and why, a particular estimate of R is appropriate in any case.
Ideas presented here benefited from discussion with Ryan Earley and Mark Briffa at a workshop funded by a BBSRC US partnering award (BB/M025799/1).
This is the author accepted manuscript. The final version is available from Wiley via the DOI in this record.
Published online 31-01-2018.