The effect of intraspecific sample size on type I and type II error rates in comparative studies.
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.
Harmon
Luke J
LJ
Department of Biology, Washington University, St. Louis, Missouri 63130, USA. harmon@zoology.ubc.ca
Losos
Jonathan B
JB
D005075:Biological Evolution; D003198:Computer Simulation; D008954:Models, Biological; D010802:Phylogeny; D018401:Sample Size; D013045:Species Specificity