I have a dataset that I do not know how to calculate pairwise distances. In sibpair linkage analysis a unit of analysis is the sibpair (2 brothers, 2 sisters, or a brother and sister). The covariate vector contains information on each of the pair (e.g., two ages, two heights, two weights). There is no way to order these covariates. Consider the two ages on two sibpairs. Let age_ij be the age for the i^th sibling in the j^th sibpair. The data matrix could be in any of the following orders: Sibpair Age1 Age2 1 age_11 age_21 2 age_12 age_22 or 1 age_21 age_11 2 age_12 age_22 or 1 age_11 age_21 2 age_22 age_12 or 1 age_21 age_11 2 age_22 age_21 We want to calculate the distance between the sibpairs since these are the units of analysis. We can arbitrarily invoke a rule (e.g., youngest is always the first age) and use standard distance measures -- but these are ad hoc and the genetic linkage people are unsatisfied with this (though it is done routinely). This is analogous to the difference between correlation and intraclass correlation. Any suggustions? Bill --- William D. Shannon, Ph.D. Assistant Professor of Biostatistics in Medicine Division of General Medical Sciences and Biostatistics Washington University School of Medicine Campus Box 8005, 660 S. Euclid St. Louis, MO 63110 Phone: 314-454-8356 Fax: 314-454-5113 e-mail: [log in to unmask] web page: http://ilya.wustl.edu/~shannon