DOI: 10.5061/dryad.zpc866t81
title: What is our power to detect device effects in animal tracking studies?

description: The use of bio-logging devices to track animal movement continues to grow
 as technological advances and device miniaturisation allow researchers to
 study animal behaviour in unprecedented detail. Balanced against the
 remarkable data that bio-loggers can provide is a need to understand the
 impact of devices on animal behaviour and welfare. Recent meta-analyses
 have demonstrated impacts of device attachment on animal behaviour, but
 there is concern about the frequency and clarity with which device effects
 are reported. One aspect lacking in many studies is assessment of the
 statistical power of tests of device effects, yet such information would
 assist the interpretation of results. We address this issue by providing
 an overview of the statistical power, as well as the Type M (magnitude)
 and Type S (sign) error rate, of tests of device effects within the avian
 tracking literature across a range of assumed effect sizes. The median
 power of statistical tests ranged from 9% to 65% across a range of assumed
 effect sizes corresponding to benchmark values for small, moderate and
 large effects (d = 0.2, 0.5, 0.8 respectively). Moreover, when using
 effect sizes derived from previous a meta-analysis (d = 0.1) median power
 was only 6%.  When assuming smaller effect sizes, statistical
 tests were characterised by high Type M and Type S error rates, suggesting
 that statistically significant results of device effects will tend to
 exaggerate the size of such effects and may estimate the sign of an effect
 in the wrong direction. Well-designed tracking studies will reduce device
 effects to low levels and consequently issues associated with low power
 will be commonplace. Nevertheless, assessment of device effects remains
 important, particularly when embarking on novel tracking studies. We
 recommend that statistical tests of device effects are reported clearly
 and are routinely accompanied by assessment of statistical power,
 including Type M and Type S errors, based upon realistic external
 estimates of effect size. Reporting the statistical power can help avoid
 the pitfalls of overstating results from individual studies, shift the
 emphasis to accurate reporting of effect sizes and guide decisions about
 the ethical impacts of device attachment.  
description: Data covers extraction of effect sizes from avian tracking
 literature with effect sizes ultimately reported using absolute values of
 Cohen's <em>d</em> together with the associated standard
 error around this effect size. Standard errors were subsequently used
 within the R 'retrodesign' package to estimate statistical
 power, Type M error rate and Type S error rate to a range of assumed
 effect sizes (<em>d</em> = 0.1, 0.2, 0.5 &
 0.8).
description: Cohen's <em>d </em>is reported as absolute,
 non-negative values. See also: Bodey et al. (2018).
   Bodey, T. W., Cleasby, I. R., Bell, F.,
 Parr, N., Schultz, A., Votier, S. C., & Bearhop, S. (2018). A
 phylogenetically controlled meta‐analysis of biologging device effects on
 birds: Deleterious effects and a call for more standardized reporting of
 study data. <i>Methods in Ecology and
 Evolution</i>, <i>9</i>(4), 946-955.