430 
Journal of Agricultural Research 
Vol. V, No. io 
tion might prove a less valuable and reliable indicator. This may 
possibly be so, though up to the present time no definite evidence on the 
point has appeared. Another point which occurs to one is that possibly 
a better measure of the winter cycle of productivity (this being the bio¬ 
logical entity we attempt to measure by the record of production to March 
i) might be obtained by using the egg production of a bird up to the time 
when it has attained a definite age. Fowls are hatched at different dates, 
while March i is a fixed point in time. Birds hatched at different times 
will be of different ages at March i of their pullet year. Will the egg 
production prior to the attainment of a definite age by a bird give a better 
measure of her winter cycle than the production prior to a fixed date with¬ 
out regard to age, except so far as this is involved in having the birds all 
hatched within a certain limited season ? It is the purpose of this paper 
to present some data on this question. 
Specifically the material here presented has to do with the suggestion 
that the egg production up to 300 days of age of the bird gives a better 
measure of the winter cycle than does the production to March 1, since an 
age of 300 days will include the winter cycle, and will also allow for differ¬ 
ences due to variation in date of hatching. Biometrically we can readily 
test this question in two ways: On the one hand, we can determine the 
correlation between the winter production as defined by the writer (to 
March 1) and the production to 300 days of age, on the other hand. If 
this correlation is low, it will mean that one of the measures is probably 
sensibly better than the other. If, on the other hand, the correlation is 
very high, differing but little from perfect correlation, it will indicate, 
so far as it goes, that there is little to choose between the two measures. 
In the second place, we may examine the variabilities biometrically. 
On theoretical grounds that measure of a character is best, other things 
being equal, which exhibits the smallest relative variability. 
Evidence along these lines derived from extensive trap-nesting experi¬ 
ments is presented in the following tables. The data cover three con¬ 
secutive years. Two correlation tables are presented for each year: One 
including the total flock of that year regardless of breed distinctions, the 
other including only pure Barred Plymouth Rocks. The total flocks 
were made up of various crossbred birds used in Mendelian experiments, 
in addition to the pure Barred Plymouth Rocks. All birds included in 
the tables are pullets—i. e., they were hatched in the spring of the year 
indicated in the caption of the table. The computations were made 
by Mr. John Rice Miner, staff computer of the Biological Laboratory. 
See Tables I to VI. 
