BIOMETRIC IDEAS AND METHODS 71 



inheritance from studies involving the correlation 1 

 method ajone is futile, because the coefficient 

 of correlation in such studies can only tell us of 

 the existence and degree of an orderly differentia- 

 tion or heterogeneity in the material collected 

 together in the correlation table. To determine 

 definitely whether the basis of the heterogeneity 

 is inheritance, recourse must be had to pedigree 

 analysis in terms of individuals and of families. 

 Of course it will be true in many cases in actual 

 practice that general considerations make it a 

 priori highly probable or even certain that the 

 basis of an observed heterogeneity is inheritance. 

 In such cases the coefficient of correlation may 

 be said to indicate the existence of inheritance, 

 though not to measure its intensity. But the 

 first and fundamental demonstration that a charac-j 

 ter is inherited in a given group of individuals 

 must always rest upon some other basis than 

 coefficients of correlation alone. The essential 

 point here made regarding the inherent difficulty 

 in the interpretation of correlation coefficients, 

 has been very ably discussed by G. Udny Yule. 1 

 I am in entire agreement with his position. 



The general purpose of this discussion regarding 

 the study of inheritance has been to show, by a 

 concrete example, how erroneous biological assump- 



1 Yule, G. Udny. "On the Interpretation of Correlations be- 

 tween Indices or Ratios." Jour. Roy. Stat. Soc, Vol. LXXIII, pp. 

 641-647, 1910. 



