HEREDITY 



489 



If there were no regression, that is, if the offspring followed 

 fully the lead of the parent, then parents above the mean would 

 have offspring equally above the mean ; that is to say, parents 

 69 inches high (one inch above the racial mean) would have 

 children also one inch above the mean, and parents two inches 

 above the mean would have children also two inches above the 

 mean, or 70 inches in height. In this way, were there no 



FIG. 45. Diagram representing regression 



regression, these points would lie in a line M'OM, with a devia- 

 tion of 45 from the vertical. 



But regression is a fact, and the children of /o-inch parents 

 are not 70 inches tall but something less, and so on for other 

 values ; so that, when the true means are platted as calculated 

 from the horizontal arrays of the regression table, and then 

 connected by the best-fitting straight line, this line N f ON does 

 not coincide with M'OM, as it would were there no regression. 

 This is known as the regression line, and its slope is the 

 measure of the pull of parental heredity. The measure of this 



