HISTORY OF WHEAT PRODUCTION IN NEW ZEALAND 123 
STANDARD DEVIATION OF PRICES = A/- Bae 
= 504.21 
= 22.45 
STANDARD DEVIATION OF SUPPLY = a/ 53.008 
= 1151 
= 33.93 
—15.151 
CO-EFFICIENT OF CORRELATION = 96x 90.45x 33.93 
= — .440 
— (.440)? x .6745 
PROBABLE ERROR = er ae 
= .079 
price. Such influences as the land boom of the ‘‘seven- 
ties,’’ the depression of the ‘‘eighties,’’ the South African 
War, also tended to disturb this natural tendency. The 
nature and extent of this influence is reserved for special 
study in the following chapter, but it is expedient here 
to point out that our co-efficient of correlation is not 
remarkably low relative to circumstances, and since the 
probable error is comparatively low we may regard the 
establishment of correlation as a practical certainty. 
The accompanying graph* showing the relation between 
price and area under wheat is interesting as illustrating 
the influence of price movements on the practice of our 
farmers in regard to wheat growing. Years of high 
prices are almost invariably followed by increases in the 
area sown, and low prices similarly exert an influence 
in reducing the area. 
8. Competition of other Industries for the Use 
of the Land. 
1. Sheep Farming.—In dealing with the general 
history of wheat production references were made to 
*See page 125. 
