289 



Prediction of annual production from the sum of two monthly records 



Before considering the results of equations for the prediction of annual 

 production from the combined record of two or more months, some general 

 questions of theory must be considered. 



If the egg production of each individual month be correlated with that 

 pf the whole year it would seem that a better prediction of the annual 

 total may be made from the record of two or more individual monthly 

 records than from one month s record only. This is a point emphasized 

 by CARD (1917) who has correlated the total production of groups of 

 nonths with the annual yield. 



There are several points to be taken into consideration here. First, 

 it should be clear that the superiority of a group of months for predicting 

 the annual yield of a bird is to a considerable extent due to the fact that 

 the records of these months are included in the annual total. Thus in 

 predicting annual total from November performance, the November record 

 is included in the annual total. In predicting from November, December 

 ind January production the records of these three months are included 

 in the annual total. As far as their own contribution is concerned, predic 

 tion can be made with absolute certainty. The importance of this factor 

 vvould be especially great during the spring months when the number of 

 3ggs laid by practically all birds is high. If the principle of an increase 

 n the number of months upon which prediction is to be based be extended 

 :o its limit, it is clear that the annual total can be predicted with exactness 

 : rom the record of twelve months. The importance of this factor was 

 &quot;ully recognized in our second publication (HARRIS, BLAKESLEE and KIRK- 

 PATRICK 1918), in which we determined the correlation between the pro 

 duction of each individual month and that of the remaining eleven months 

 :&amp;gt;f the year, as well as that between the production of the individual months 

 md the annual record. 



It is evident that it is impossible to compare directly and critically the 

 errors made in predicting annual egg production from two-month periods 

 md from single-month periods; in one case a single component only is 

 included in the first and second variable of the pair whereas in the second 

 :ase two components are involved. The problem of a direct comparison 

 &amp;gt;vill be taken up in a subsequent section. 



Second, from the economic standpoint it is clear that trap-nesting for 

 two months or three months is (disregarding initial investment) twice 

 3r three times as expensive as trap-nesting for one month. In general 

 t is important to utilize the shortest practicable period on which predic 

 tion may be based. 



GENETICS 6: My 1921 



