xliv 



Tables for Statisticians and Biometricians [XXV 



Gain by sulphate of potash. 



1904 {a) 10 cwt. 3 qr. 20 lbs. 



(6) 1 toil 10 cwt. 1 qr. 26 lbs. 



1905 ((() 6 cwt. qr. 3 lb.s. 

 (6) 13 cwt. 2 qr. 8 lbs. 



Average gain = 15-25 cwt., and the standard deviation = 9 cwt., z= 15-25/9 = 1-694.. 



Here n = 4, and Table XXV gives us 



P = -9653 + 0-94 X [46] = -9696, 

 or the odds are about 32 to 1 that the sulphate of potash is a better dressing than 

 kainite for potatoes. 



Illustration (iii). Test whether it is of advantage to kiln-dry barley seed 

 before sowing. The following table gives price of head corn in shillings per 

 quarter for 11 sowings, the first seven in 1899 and the last four in 1900. 



Not Kiln-dried 



Eiln-dried 



A 



1899 - 



1900 H 



26-5 



28 



29-5 



30 



27-5 



26 

 ^29 

 r29-5 



28-5 



30 



28-5 



26-5 



26-5 



28-5 



29 



27 



26 



26 



28-5 



28 



29 



28 







1-5 



1 



1 



0-5 







3 



1 



0-5 



1 



0-5 



Mean 



Standard Deviation 



— 



-91 

 -79 



The Gaussian curve gives 



'Wii: 



e'^^'^'dx. 



Here a;=-91/-79 = 1-1519, 



and if cc' = x/\/lj8 = 1-1519 x 2-8284 = 3-258, 



1 /■3-23S .,„ 



P = ^ e-^-"" dx', 



V27r J -00 



which evaluated by Table II, p. 6, gives 



P = -99944, 



or the odds are 2845 to 1 in favour of not kiln-drying seed barley. 



