No. 614] 



EGG PRODUCTION 



the minimum is represented by a single egg laid during 

 the winter and that one at the beginning of the winter 

 period, no correlation would exist if the scatter is per- 

 fect between these extremes. Experience shows, how- 

 ever, that conditions approached by the maximum rate 

 of production are much more common than those rep- 

 resented by the minimum so that the coefficient, even 

 though it has a high value, shows only that the rate of 

 production is comparatively uniform. It does not prove 

 that the flock is composed exclusively of high producers, 

 for, since it is an average figure, the flock may still con- 

 tain some true mediocre producers. A certain degree of 

 correlation, however, is to be expected in any flock, so that 

 the mere existence of a small positive correlation is of 

 little value, though a low value for the coefficient would 

 imply that there was considerable variability in rate of 

 production. It is quite clear that if a considerable per- 

 centage of the flock made records like those shown in Fig. 

 12, the variability in rate would be much greater than 

 observed, and the coefficient of correlation between length 

 of laying period and number of eggs would be smaller. 



Size,— Size does not of itself seem to have any specific 

 relation to a bird's ability to lay because birds of all sizes 

 may lay equally well once they have started. It is true, 

 of course, that very large birds rarely make high records, 

 but as there are very few large birds, the chance for a 

 combination between very high egg production, itself un- 

 common, and large size is rather remote. The converse, 

 however, is not apparently true, for small birds fre- 

 quently make good records. Since, however, birds that 

 are too small are not desired by poultrymen while as a 

 rule large birds are considered desirable, very small birds 

 are not often trap-nested, so that a strict comparison is 

 at present impossible. 



In another way size seems to exert some influence on 

 the record a hen makes. On the average, as shown by 

 the coefficient of correlation between age at first egg and 

 weight, birds of large size reach this size later in life 



