CORRELATION 107 
affected, as regards their value for representing quanti- 
tatively a hereditary relationship between two indi- 
viduals, by the fact that the statistics from which they 
are derived show the existence of a marked correlation 
between husbands and wives in point of stature, 
amounting, indeed, to as much as 0:28—the result 
of what is technically described as selective mating. 
In the absence of such a relation between the statures of 
the parents, the correlation between parent and child 
might be expected to be distinctly less than that 
between pairs of brothers or sisters. 
The term correlation replaces to some extent the 
older term yvegression employed by Galton. When 
speaking of regression the facts already described are 
regarded from a slightly different point of view. It 
is sometimes found convenient to speak of the regres- 
sion of the mean stature of an array of sons toward 
the mean of the general population, instead of speaking 
of the correlation between the filial mean and the 
value of the parental class. 
Regression represents the extent to which the 
average son is more like the mean of the general 
population than his father is. Correlation, on the 
other hand, indicates the amount by which the son is 
more like his parent than he is to the average of the 
general population. Thus, instead of being exactly 
like their parents, children are said to show regression 
towards the mean of the general population to which 
both parents and children belong. 
In a case where the mean height of the fathers is 
identical with the mean height of the sons examined, 
