treestats (version 1.70.5)

gamma_statistic: Gamma statistic

Description

The gamma statistic measures the relative position of internal nodes within a reconstructed phylogeny. Under the Yule process, the gamma values of a reconstructed tree follow a standard normal distribution. If gamma > 0, the nodes are located more towards the tips of the tree, and if gamma < 0, the nodes are located more towards the root of the tree. Only available for ultrametric trees.

Usage

gamma_statistic(phy)

Value

gamma statistic

Arguments

phy

phylo object or ltable

References

Pybus, O. G. and Harvey, P. H. (2000) Testing macro-evolutionary models using incomplete molecular phylogenies. Proceedings of the Royal Society of London. Series B. Biological Sciences, 267, 2267–2272.

Examples

simulated_tree <- ape::rphylo(n = 10, birth = 1, death = 0)
gamma_statistic(simulated_tree) # should be around 0.
if (requireNamespace("DDD")) {
  ddd_tree <- DDD::dd_sim(pars = c(1, 0, 10), age = 7)$tes
  gamma_statistic(ddd_tree) # because of diversity dependence, should be < 0
}