Page:Biometrika - Volume 6, Issue 1.djvu/22

view of the well-known fact that the varieties which have a high yield tend to produce soft corn, it is interesting to see how much evidence the experiments afford as to the correlation between softness and fertility in the same variety.

Further, Mr Hooker^[1] has shown that the yield of wheat in one year is largely determined by the weather during the preceding harvest. Dr Voelcker’s results may afford a clue as to the way in which the seed is affected, and would almost justify the selection of particular soils for growing seed wheat^[2].

The figures are as follows, the yield being expressed in grammes per pot.

​
Year
​ 1899 1900 1901 Average Standard
Deviation $z$ ​
Soil
​ Light Heavy Light Heavy Light Heavy ​ Yield of corn from soft seed 07.85 08.89 14.81 13.55 07.48 15.39 11.328 Yield of„ corn from„ softhard seed„ 07.27 08.32 13.81 13.36 07.97 13.13 10.643 ​ ​
Difference
​ +.58 +.57 +1.00 +.19 −.49 +2.26 +.685 .778 .88 ​ Yield of straw from soft seed 12.81 12.87 22.22 20.21 13.97 22.57 17.442 Yield of„ straw from„ softhard seed„ 10.71 12.48 21.64 20.26 11.71 18.96 15.927 ​ ​
Difference
​ +2.10 +.39 +.78 −.05 +2.66 +3.61 +1.515 1.261 1.20

If we wish to find the odds that soft seed will give a better yield of corn on the average, we divide the average difference by the standard deviation, giving us

$z=.88$.

Looking this up in the table for $n=6$ we find $p=.9465$ or the odds are .9465:535, about 18:1.

Similarly for straw $z=1.20$, $p=.9782$, and the odds about 45:1.

In order to see whether such odds are sufficient for a practical man to draw a definite conclusion, I take another set of experiments in which Dr Voelcker compares the effects of different artificial manures used with potatoes on the large scale.

The figures represent the difference between the crops grown with the use of sulphate of potash and kainit respectively in both 1904 and 1905.

cwt. qr. lb. ton cwt. qr. lb. 1904 + 10 3 20 : + 1 10 1 26 (two experiments in each year). 1905 + 06 0 3 : + 13 2 8

1. Journal of Royal Statistical Society, 1907.
2. And perhaps a few experiments to see whether there is a correlation between yield and ‘mellowness’ in barley.