SHORTER ARTICLES AND DISCUSSION 



FURTHER NOTES REGARDING SELECTION INDEX 

 NUMBERS 1 



The purpose of the present communication is to correct and 

 extend a former paper from this laboratory 2 dealing with the 

 use of index numbers in mass selection operations. In the cor- 

 respondence which the writer has had with various workers re- 

 garding that paper it would appear that a point which it was 

 intended should be emphasized has been rather overlooked. 

 This is that the examples of index numbers therein given for 

 sweet corn and for poultry were intended merely to illustrate 

 the principles involved. They were not put forward as the best 

 formulae which could be devised, even for the organisms dis- 

 cussed. It was pointed out that the particular formula to be 

 used should be devised by each worker to fit his particular needs. 

 Apparently a number of workers have adopted without change 

 the formula? given in our first paper. I wish again to empha- 

 size that unless these happen to meet exactly the particular needs 

 of the breeder, it is highly desirable that he develop formulas of 

 his own, involving the same general principle, but adapted to 

 Ms special conditions. 



I. Correction of an Error in the Formula of a Selection 

 Index Number for Corn 



In our first paper there is an error in one of the equations for 

 the se lection index for sweet corn (loc. cit., pp. 397-399). 



This error has given trouble to some workers desiring to use 

 this index number in breeding work with corn, and may cause 

 confusion in the future. Doubtless some of those who have used 

 the index in their work have, like the writer, made for them- 

 selves the somewhat obvious correction. Nevertheless, to insure 

 that there may be no further confusion it seems desirable to pub- 

 lish a formal correction. 



1 Papers from the Biological Laboratory of the Maine Experiment 



