NATURE OF STATISTICAL KNOWLEDGE 83 



is confined to the particular group on which the 

 measurement is made, and to that group alone, 

 and to a single instance (in time) the knowledge 

 gained is precise. It is a part of the description 

 of the attributes of that group. When we pass 

 from that particular group to other groups or 

 individuals our results are no longer precise, but 

 inferential, and the probable errors tell us some- 

 thing about the degree to which the inference is 

 trustworthy. 



Summarizing the results of the above analysis, 

 we see that the statistical method can 



1. Furnish precise descriptive knowledge about 

 groups. This knowledge is of various sorts. It 

 is definite and precise so long as attention is con- 

 fined solely to the particular group and the par- 

 ticular instance on which it is based. 



2. The knowledge gained by the statistical 

 method, as we have analyzed it above, precise 

 though it may be, 'pertains to the group and not to 

 the individual. It is exact knowledge about the 

 composition, or attributes, or contingencies of 

 masses or groups. 



3. This ability to describe groups in terms of 

 the groups' own attributes, which is an unique 

 property of the statistical method, is extremely 

 useful in the practical conduct of scientific in- 

 vestigations. It makes the statistical method an 

 absolutely essential adjunct to every other scien- 

 tific method, and particularly to the experimental. 



