ASSORTATIVE MATING IN MEN 479 



2. The Measurement of Assortative Mating 



The precise meaning of the term " assortative mating " may perhaps 

 be made a little clearer in the process of explaining how the similarity 

 or dissimilarity of husband and wife is measured. 



Suppose a most highly refined socialistic community should set about 

 to equalize as nearly as possible not only men's labor and their recom- 

 pense, but the quality of their wives. It would never do to allow indi- 

 viduals to select their own partners — superior cunning might result in 

 some having mates above the average desirability, which would be 

 socially unfair ! 



The method adopted would be to write the names of an equal number 

 of men and women officially condemned to matrimony on cards, and to 

 place those for men in one lottery wheel and those for women in another. 

 The drawing of a pair of cards, one from each wheel, would then replace 

 the " present wasteful system " of " competitive " courtship. If the 

 cards were thoroughly shuffled and the drawings perfectly at random, 

 we should expect only chance resemblances between husband and wife 

 for age, stature, eye and hair color, temper and so on ; in the long run, 

 a wife would resemble her husband no more than the husband of some 

 other woman. In this case, the mathematician can give us a coefficient 

 of resemblance, or of assortative mating, which we write as zero. The 

 other extreme would be the state of affairs in which men of a certain 

 type (that is to say men difEering from the general average by a definite 

 amount) always chose wives of a definite type; the resemblance would 

 then be perfect and the correlation, as we call it, would be expressed 

 by a coefficient of 1. 



Fortunately, the meaning of correlation can be illustrated by a char- 

 acter for which the reader knows that there is a high degree of assorta- 

 tive mating. The table^" shows the age of bride and groom in 2,500 

 Chicago couples. The swarm of figures showing the frequencies of 

 different combinations spreads diagonally across the table, demonstrating 

 that while men or women of any class marry consorts of varying ages, 

 there is a pronounced tendency for individuals of the same relative age^^ 

 to mate. From such a table the statistician calculates the equation to a 

 straight line (or to a curve of a higher order) which describes approxi- 

 mately the change in the average age of brides associated with increase 

 in the age of the grooms. The diagram (Fig. 1) shows that the agree- 

 ment of the theoretical line with the empirical means is very close 

 indeed. ^^ Or he may express the closeness of correlation quite inde- 

 pendently of the absolute values of the two characters on the scale of 



" From a paper by F. E. Lutz, ' ' Assortative Mating in Man, ' ' Science, 

 N. S., Vol. 22, pp. 249-250, 1905. 



" Since women marry younger than men, relative, not absolute, age must be 

 specified. 



" Such differences as occur are probably due to errors of random sampling. 



