Analysis of marital structure in Massachusetts using repeating pairs of surnames

Analysis of surnames from marriages is now a well-established method in the study of marital and genetic structure. Traditional methods of partitioning inbreeding into random and nonrandom components rely on the total number of isonymous marriages. Because this number is often low, standard errors of inbreeding estimates tend to be high. Lasker and Kaplan (1985) devised a method that circumvents this problem by focusing on the total number of repeating pairs (RP) of surnames among marriages. The observed value of RP can be compared with the value expected at random (RPr) to assess patterns of subdivision within a population. The RP method is applied here to data from 3431 marriages that took place from 1800 to 1849 in 4 Massachusetts towns. The level of excess RP [(RP-RPr)/RPr] is positively associated with population size and exogamy rate. These results indicate a tendency for greater relative subdivision in larger, more exogamous populations. One possible reason for increased subdivision is preferential marriage by social class, although adequate data are not available for a test of this hypothesis.