OLS branch length estimates

The ordinary least squares estimate of a branch length (b) is given by

$image\olsbranchlenest_d1.gif$

where dij is the pairwise distance between sequences i and j. The coefficients wijs depend on whether the branch under consideration is internal or external.

Coefficients wijs for an internal branch

$image\olsbranchlenest_d2.gif$

where, mA, mB, mC, and mC are the numbers of sequences in clusters A, B, C, and D, respectively.

Coefficients wijs for an external branch

$image\olsbranchlenest_d3.gif$

where, mA and mB are the numbers of sequences in clusters A and B.