Vol.. 7, 1921 
GENETICS: J. A. HARRIS ET AL. 
215 
the unknown, we have calculated equations based upon the data of the 
International Ijgg Laying Contest at Storrs, Conn., during the six contest 
years, 1911-1917, inclusive. We have then used these equations to pre- 
dict the annual production (and the production of groups of months) for 
the birds of the 19 17-' 18 contest, using as a basis of prediction the individ- 
ual months of the laying year separately, pairs of successive months and 
groups of three months. Our conclusions concerning the value of the 
equations depend, therefore, not upon a priori considerations but upon the 
results of actual tests of accuracy of prediction for series which were un- 
known as far as the determination of the constants of the equations is 
concerned. 
Consider first of all the results of the attempts to predict the annual 
egg production of 415 White Leghorn birds observed at Storrs from Nov. 
1, 1917 to Oct. 31, 1918 from the records of a single month's production. 
The results of the three criteria of accuracy of prediction are summa- 
rized in table 1. 
TABLE 1 
Errors op Prediction of Annual Egg Production from the Records 
of Individual Months 
MONTH 
AVERAGE 
DEVIATION 
AVERAGE 
DEVIATION 
SQUARE ROOT OP MEAN 
USED AS 
WITH REGARD TO SIGN 
WITHOUT REGARD TO SIGN 
SQUARE 
DEVIATION 
BASE OP 
Actual 
Percentage 
Actual 
Percentage 
Actual 
Percentage 
PREDICTION 
deviation 
deviation 
deviation 
deviation 
deviation 
deviation 
November 
+ 2.39 
1.52 
29.59 
18.78 
38.65 
24.52 
December 
— 0.49 
0.31 
29.26 
18.57 
37.61 
23.86 
January 
+ 2.58 
1.64 
30.09 
19.09 
38.77 
24.60 
February 
+ 0.06 
0.04 
27.28 
17.31 
34.70 
22.02 
March 
— 1.63 
1.03 
27.95 
17.73 
34.28 
21.75 
April 
— 6.23 
3.95 
28.72 
18.22 
35.31 
22.40 
May 
+ 7.02 
4.45 
28.62 
18.16 
35.89 
22.77 
June 
— 5.21 
3.31 
29.03 
18.42 
36.53 
23.18 
July 
— 5.27 
3.34 
28.35 
17.99 
35.89 
22.77 
August 
— 0.82 
0.52 
26.87 
17.05 
34.34 
21.79 
September 
+ 4.78 
3.03 
24.78 
15.72 
32.94 
20.90 
October 
+ 3.95 
2.51 
27.37 
17.37 
36.47 
23.14 
Considering first of all the absolute values we note that the average 
errors with regard to sign are generally low. Thus the prediction from No- 
vember and from January production gives on the average 3 eggs too many 
for the year. For December, February, March and August the predic- 
tion is in error by less than 2 eggs. The values predicted from April, May, 
June, July, September and October records are from 4 to 7 eggs in error. 
The average deviations without regard to sign are of course much larger 
since they constitute a measure of the error of prediction of the records of 
individual birds. They range from 24.8 to 30.1 eggs. The significance 
of errors of this magnitude will be more clearly brought out later. 
The square root of mean square deviation also shows considerable regu- 
