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Journal ArticleDOI

Unrepeatable repeatabilities: a common mistake

C. M. Lessells, +1 more
- 01 Jan 1987 - 
- Vol. 104, Iss: 1, pp 116-121
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TLDR
The correct calculation of repeatability is outlined, a common mistake is pointed out, how the incorrectly calculated value relates to repeatable values is shown, and a method for checking published values and calculating approximate repeatability values from the F ratio is provided.
Abstract
-Repeatability is a useful tool for the population geneticist or genetical ecologist, but several papers have carried errors in its calculation We outline the correct calculation of repeatability, point out the common mistake, show how the incorrectly calculated value relates to repeatability, and provide a method for checking published values and calculating approximate repeatability values from the F ratio (mean squares among groups/ mean squares within groups) Received 6 February 1986, accepted 25 August 1986 REPEATABILITY is a measure used in quantitative genetics to describe the proportion of variance in a character that occurs among rather than within individuals Repeatability, r, is given by: r = (VG + VEg)/ VP, (1) where VG is the genotypic variance, VEg the general environmental variance, and Vp the phenotypic variance (Falconer 1960, 1981) In addition to its use in assessing the reliability of multiple measurements on the same individual, repeatability may be used to set an upper limit to the value of heritability (Falconer 1960, 1981) and to separate, for instance, the effects of "self" and "mate" on a character such as clutch size (van Noordwijk et al 1980) Repeatability is therefore a useful statistic for population geneticists and genetical ecologists Recently, we have noticed an increasing number of published papers and unpublished manuscripts in which repeatability was miscalculated Our purpose is fivefold: (1) to outline the correct method of calculating repeatability; (2) to point out a common mistake in calculating repeatability; (3) to show how much this mistake affects values of repeatability; (4) to provide a quick way of checking published estimates, and to calculate an approximate value of repeatability from published F ratios and degrees of freedom; and (5) to make recommendations for authors, referees, editors, and readers to prevent the promulgation and propagation of incorrect repeatability values in the literature CALCULATION OF REPEATABILITY Repeatability is the intraclass correlation coefficient (Sokal and Rohlf 1981), which is based on variance components derived from a one-way analysis of variance (ANOVA) The intraclass correlation coefficient is given by some statistical packages; otherwise it can be calculated from an ANOVA ANOVA is described in most statistics textbooks (eg Sokal and Rohlf 1981; Kirk 1968 gives a detailed treatment of more complex designs of ANOVA), so we will not repeat it here, but give the general form of the results from such an analysis in Table 1 Repeatability, r, is given by r = sA / (S + SA)' (2) where S2A is the among-groups variance component and s2 is the within-group variance component These variance components are calculated from the mean squares in the analysis of variance as:

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Citations
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Predictable males and unpredictable females: sex difference in repeatability of parental care in a wild bird population.

TL;DR: A need is suggested for a new theoretical framework that encompasses variation in the predictability and plasticity of parental investment by individuals in a sexually dimorphic species, the house sparrow, Passer domesticus.
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Offspring sex ratio is related to male body size in the great tit (Parus major)

TL;DR: The proportion of sons in the brood increased significantly with male tarsus length and also, though not significantly, with the size of the breast stripe, confirming the assumption of a father-offspring correlation.
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By hook or by crook? Morphometry, competition and cooperation in rodent sperm.

TL;DR: The results suggest that in rodents sperm cooperation is more widespread than assumed so far and highlight the importance of diploid versus haploid selection in the evolution of sperm design and function.
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Oxidative damage and anti-oxidant capacity in two migratory bird species at a stop-over site.

TL;DR: Data are the first of this kind in wild birds in a migratory context and suggest that individuals in better condition are exposed to lower oxidative stress, providing an indirect evidence of the oxidative cost caused by prolonged flights.
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Dynamics of parasitemia of malaria parasites in a naturally and experimentally infected migratory songbird, the great reed warbler Acrocephalus arundinaceus.

TL;DR: The experiment demonstrated that P. ashfordi and P. relictum lineages differ substantially in several life-history traits and that individual hosts show substantial differences in responses to these infections, and the intensity of parasitemia for individual hosts was highly repeatable suggesting variation between the host individuals in their genetic or acquired control of the infections.
References
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Book

Introduction to quantitative genetics

TL;DR: The genetic constitution of a population: Hardy-Weinberg equilibrium and changes in gene frequency: migration mutation, changes of variance, and heritability are studied.
Book

Experimental Design: Procedures for the Behavioral Sciences

Roger E. Kirk
TL;DR: This chapter discusses research strategies and the Control of Nuisance Variables, as well as randomly Randomized Factorial Design with Three or More Treatments and Randomized Block Factorial design, and Confounded Factorial Designs: Designs with Group-Interaction Confounding.
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