PROBLEM OF NURTURE AND NATURE 



47 



would only be -50, the value of the correlation of an individual with 

 a single parent. 



If we suppose a system in which the environmental correlations 

 are roughly of the same order, and the inter-environmental correlations 

 approximately of value e, we shall be able to deduce approximately 

 the multiple correlation of the individual with n factors of environment 

 by multiplying the mean environmental correlation by the quantity 



i. The following table provides the value of this 



i -\- . \n i) 



expression for values of n and of the mean inter-environmental 

 correlation e. 



TABLE IV. 



Table of multipliers for estimating approximately the effect 

 of combining n environmental factors. 



Number of Environmental Factors 



Now this table brings out some exceedingly interesting points. 

 In the first place if the inter-environmental correlations were as low 

 as -30, we should not double the multiple correlation of the individual 

 and his environment by taking into account an infinity of environ- 

 mental factors. If the inter-environmental correlations were as high 

 as -60, we should only add about 30 % to the mean value of the 

 correlations of the individual's character with the environmental 

 factors. It will be seen how soon we reach a limit to the sensible 

 increase of association obtained by combining numerous environmental 

 factors even if these be only moderately correlated together. 



1 See Biometrika, vol. x, p. 181. 



