Comparative studies have increased greatly in number in recent years due to advances in statistical and phylogenetic methodologies. For these studies, a trade-off often exists between the number of species that can be included in any given study and the number of individuals examined per species. Here, we describe a simple simulation study examining the effect of intraspecific sample size on statistical error in comparative studies. We find that ignoring measurement error has no effect on type I error of nonphylogenetic analyses, but can lead to increased type I error under some circumstances when using independent contrasts. We suggest using ANOVA to evaluate the relative amounts of within- and between-species variation when considering a phylogenetic comparative study. If within-species variance is particularly large and intraspecific sample sizes small, then either larger sample sizes or comparative methods that account for measurement error are necessary.
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1 December 2005
THE EFFECT OF INTRASPECIFIC SAMPLE SIZE ON TYPE I AND TYPE II ERROR RATES IN COMPARATIVE STUDIES
Luke J. Harmon,
Jonathan B. Losos
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Evolution
Vol. 59 • No. 12
December 2005
Vol. 59 • No. 12
December 2005
independent contrasts
measurement error
PHYLOGENETIC COMPARATIVE METHOD
population variation
statistics