NOTES AND LITEEATURE 



AN OUTLINE OF CURRENT PROGRESS IN THE THEORY 

 OF CORRELATION AND CONTINGENCY 



Workers in the physical sciences realized long ago that cer- 

 tain progress depended upon the precision of their instruments 

 of measurement and the adequacy of their methods of mathe- 

 matical description and analysis. Biologists, here and there, are 

 beginning to see the importance of the analytical as well as of the 

 observational tools. Among the analytical formulae none are 

 of greater usefulness than those for measuring interdependence. 

 It may not be out of place, therefore, to sketch in simple terms 

 for the benefit of those who are interested in the methods only as 

 a means to an end, the progress which is being made in the per- 

 fection of these instruments of research. 



The term current as used in these paragraphs is made more 

 comprehensive than is conventional; some of the citations are 

 four or even more years old. The elasticity of the term is justi- 

 fied in dealing with the literature of a field in which progress is 

 particularly difficult and in which actual contributions are incor- 

 porated but slowly into the working technique of the biologist. 

 Indeed, biologists as a class still think of correlation as synony- 

 mous with the classical product-moment method. How erroneous 

 this impression is will appear in the following pages. 



The purpose of this review is therefore to indicate in non- 

 mathematical terms easily comprehensible to biological readers 

 the lines of advances in the theory of the measurement of inter- 

 dependence in order that they may the more easily select for 

 dealing with their actual data, formulas of the existence of 

 which they might otherwise be unaware. 



The progress which we have to consider has been along four 

 different lines : 



(a) In the simplification of methods of computation in the 

 case of familiar formula?. (6) In the development of entirely 

 new formulas applicable to data of particular sorts, (c) In the 

 determination of the corrections to be applied for grouping into 

 " broad categories." (d) In partial correlation, multiple cor- 

 relation, and the correlation of indices and increments. 



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