Hayes and Garber - Cucurbit Breeding

56 BREEDING CROP PLANTS
four plots. Using this figure as a basis, a direct comparison
may be made between the average yield of any two strains in
terms of their probable errors. To carry our hypothetical
problem still further, suppose the average yield of four plots of
strain A was 20 bu. while that of strain B was 26 bu. As the
probable error of each average is 2 bu., and the probable error of
a difference is
equal to the square root of the sum of the squares
of the probable errors of the two quantities, we would have
26 + 2
20 + 2
6 VTT^ or 6 2.8
The difference is only a little more than two times its probable
TABLE X. PROBABILITY OF OCCURRENCE OF STATISTICAL DEVIATIONS OF
DIFFERENT MAGNITUDES RELATIVE TO THE PROBABLE ERROR
Deviation
divided by
P.E.