pic {ape} | R Documentation

## Phylogenetically Independent Contrasts

### Description

Compute the phylogenetically independent contrasts using the method described by Felsenstein (1985).

### Usage

    pic(x, phy, scaled = TRUE, var.contrasts = FALSE,
        rescaled.tree = FALSE)

### Arguments

`x` | a numeric vector.
`phy` | an object of class `"phylo"`.
`scaled` | logical, indicates whether the contrasts should be scaled with their expected variances (default to `TRUE`).
`var.contrasts` | logical, indicates whether the expected variances of the contrasts should be returned (default to `FALSE`).
`rescaled.tree` | logical, if `TRUE` the rescaled tree is returned together with the main results.

### Details

If `x` has names, its values are matched to the tip labels of `phy`, otherwise its values are taken to be in the same order than the tip labels of `phy`.

The user must be careful here since the function requires that both series of names perfectly match. If both series of names do not match, the values in the `x` are taken to be in the same order than the tip labels of `phy`, and a warning message is issued.

### Value

either a vector of phylogenetically independent contrasts (if `var.contrasts = FALSE`), or a two-column matrix with the phylogenetically independent contrasts in the first column and their expected variance in the second column (if `var.contrasts = TRUE`). If the tree has node labels, these are used as labels of the returned object.

If `rescaled.tree = TRUE`, a list is returned with two elements named “contr” with the above results and “rescaled.tree” with the tree and its rescaled branch lengths (see Felsenstein 1985).

### Author(s)

Emmanuel Paradis

### References

Felsenstein, J. (1985) Phylogenies and the comparative method. American Naturalist, 125, 1–15.

### See Also

`read.tree`, `compar.gee`, `compar.lynch`, `pic.ortho`, `varCompPhylip`

### Examples

    ### The example in Phylip 3.5c (originally from Lynch 1991)
    cat("((((Homo:0.21,Pongo:0.21):0.28,",
       "Macaca:0.49):0.13,Ateles:0.62):0.38,Galago:1.00);",
       file = "ex.tre", sep = "\n")
    tree.primates <- read.tree("ex.tre")
    X <- c(4.09434, 3.61092, 2.37024, 2.02815, -1.46968)
    Y <- c(4.74493, 3.33220, 3.36730, 2.89037, 2.30259)
    names(X) <- names(Y) <- c("Homo", "Pongo", "Macaca", "Ateles", "Galago")
    pic.X <- pic(X, tree.primates)
    pic.Y <- pic(Y, tree.primates)
    cor.test(pic.X, pic.Y)
    lm(pic.Y ~ pic.X - 1) # both regressions
    lm(pic.X ~ pic.Y - 1) # through the origin
    unlink("ex.tre") # delete the file "ex.tre"

[Package ape version 4.1 Index]