loo Social Environment 



included in as early a census as that of 1840. 

 These precautions have been taken ; and in view 

 of the decisive results obtained, any further 

 precautions seem unnecessary. 



For the benefit of those who are not familiar 

 with coefficients of correlation, a brief state- 

 ment of their meaning may be in place. It has 

 already been stated that the computing of a 

 correlation means the measurement of the ex- 

 tent of agreement existing between any two 

 related sets of data. The relationship as found 

 is expressed by a coefficient that may range in 

 value from one to minus one. The former 

 means complete agreement, zero means such a 

 lack of agreement as would usually result from 

 mere chance, and minus one means that the 

 data compared are negatively related. For 

 example, if the states were found to rank in 

 exactly the same order for density of popula- 

 tion as for fertility in noted men, the correla- 

 tion would be said to be one; if they ranked 

 in the reverse order the correlation would be 

 said to be minus one. Zero would indicate a 

 promiscuous order showing no distinct agree- 

 ment or opposition. The general meaning of 

 intermediate values is, of course, apparent. 

 More precisely, it is assumed from experience 



