chronopl {ape} | R Documentation |
This function estimates the node ages of a tree using semi-parametric method based on penalized likelihood (Sanderson 2002). The branch lengths of the input tree are interpreted as (mean) numbers of substitutions.
chronopl(phy, lambda, node.age = NULL, nodes = NULL, CV = FALSE)
phy |
an object of class "phylo" . |
lambda |
value of the smoothng parameter. |
node.age |
numeric values specifying the fixed node ages. |
nodes |
the numbers (given as negative numerics) of the nodes
whose ages are given by node.age . |
CV |
whether to perform cross-validation. |
The idea of this method is to use a trade-off between a parametric formulation where each branch has its own rate, and a nonparametric term where changes in rates are minimized between contiguous branches. A smoothing parameter (lambda) controls this trade-off. If lambda = 0, then the parametric component dominates and rates vary as much as possible among branches, whereas for increasing values of lambda, the variation are smoother to tend to a clock-like model (same rate for all branches).
`lambda' must be given. The known ages are given in `node.age', and
the correponding node numbers in `nodes'. These two arguments must
obviously be of the same length. If they are left NULL
, then
the age at the root is fixed at one.
The cross-validation used here is different from the one proposed by Sanderson (2002). Here, each tip is dropped successively and the analysis is repeated with the reduced tree: the estimated dates for the remaining nodes are compared with the estimates from the full data. For the ith tip the following is calculated:
SUM[j = 1, ..., n-2] (tj - tj[-i])^2/tj
,
where tj is the estimated date for the jth node with the full phylogeny, tj[-i] is the estimated date for the jth node after removing tip i from the tree, and n is the number of tips.
an object of class "phylo"
with branch lengths as estimated by
the function. There are two or three further attributes:
ploglik |
the maximum penalized log-likelihood. |
rates |
the estimated rates for each branch. |
D2 |
the influence of each observation on overall date
estimates (if CV = TRUE ). |
Emmanuel Paradis paradis@isem.univ-montp2.fr
Sanderson, M. J. (2002) Estimating absolute rates of molecular evolution and divergence times: a penalized likelihood approach. Molecular Biology and Evolution, 19, 101–109.
chronogram
, ratogram
,
NPRS.criterion