−1 to + 1. In this case, the correlation is +.75 or about three fourths of the distance up the scale of 0 to 1, from no resemblance to perfect identity.
To determine whether men and women tend to parity or disparity in matrimonial choice, we must, therefore, take a large number of mated pairs at random from the general population, sort them into groups according to some characteristic—quantitatively measurable whenever possible—and determine by means of the statistician's coefficient of correlation whether generally similar or dissimilar groups of men and women tend to mate, and how strong this tendency to parity or disparity is. Throughout this paper the intensity of assortative mating will be expressed by the coefficient of correlation. The reader will have to bear in mind merely that positive coefficients indicate a similarity and negative coefficients dissimilarity in husbands and wives as compared with random pairs of men and women from the population,
II. Assortative Mating for Physical Characters
The psychological basis of the popular notion that men and women seek disparity rather than parity in the stature of their mates is not far to seek. On the streets the linear wife and spherical husband, or the reverse combination, appeal to our sense of humor while the multitude of similarities pass unnoticed. Yet when lumped on the statistical scales the modal multitude may outweigh the extreme combinations whose incongruity provoke a smile as they pass to the front circle after the curtain has gone up.
With the rough statistical methods then available, Galton was unable to detect any tendency towards marriage selection with respect to stature, but Pearson on the same data as early as 1897 suspected homogamy. The results from his own more extensive family records are shown in Table II. For convenience the figures for forearm and span are also given.
- This value is perhaps a little too high. However much popular opinion may overestimate women 's reticence concerning their ages, statisticians know that even the correct age of marriage of both men and women is hard to obtain. Especial difficulty is to be expected near the extremes of the series. Those embarrassed by years may declare themselves of legal age, or even deduct a few years. Those who are not yet of legal age may falsify to obtain a license. Aa Lutz aptly remarks, these figures, "instead of telling the exact truth, show us the state of things modified somewhat by man's idea of how he thinks they had better be."
- Galton, F., "Natural Inheritance," p. 206.
- Pearson, K., Phil. Trans. Roy. Soc. Lond., A, Vol. 187, p. 273, 1897; also, "Grammar of Science," 2d ed., pp. 429-431, 1900.
- Pearson, K., and A. Lee, "On the Laws of Inheritance in Man. I., Inheritance of Physical Characters," Biometrika, Vol. 2, pp. 372-377, 1903.