If all \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}${n \choose 2}$\end{document}n2 anchors are used, the distance-sum approach becomes equivalent to the all-pairs approach and is provably statistically consistent (Theorem 3). On the other hand, using only two pairs of anchors makes the placement of anchors dependent on averages of two numbers, one of which is missing, a clearly problematic scenario. Choosing an intermediate number of anchors, while insufficient for giving proofs of consistency, clearly reduces the impact of missing values. For example, assume we have m anchors and each species is included in at most only one of those anchors. The summary distance between each pair of leaves becomes an average of m values, among which at most one may be missing.