GENERAL CONDITIONS IN NEW ZEALAND 49 



STANDARD DEVIATION OF RAINFALL = 



= 



CO-EFFICIENT OF CORRELATION = 



30x3.06x2.85 

 = +.602 



PPnmm TT TTT?T?OT? 1-(.602) X .67AJT 



PROBABLE ERROR - -/= 



=.0786 



and rainfall for that state, and a priori for the whole 

 of Australia. Fluctuations in rainfall are invariably 

 followed by fluctuations of a similar nature in yield. 



The co-efficient of correlation between these two series 

 is + -602 and the probable error only -08, so that 

 correlation may be regarded as a practical certainty, 

 according to Professor Bowley, who takes as one test 

 of correlation a probable error of less than one sixth of 

 the co-efficient of correlation. 



From the graphs for New Zealand and Australia given 

 here many interesting conclusions could be drawn, but 

 we must content ourselves with a brief summary of 

 results.* 



The correlation between yield and rainfall in Aus- 

 tralia is more vital than it is in New Zealand; because 

 Australian rainfall is so small that fluctuations either 

 way greatly affect the productivity of the soil. In New 

 Zealand, on the contrary, it is only in very exceptional 

 circumstances that rainfall is so low as to interfere 

 greatly with productivity, while it is generally of such 

 an amount that an increase does not add much to the 

 yield of produce. 



This conclusion adds further to the contention that 

 from the point of view of rainfall, New Zealand enjoys 

 a differential advantage in wheat production. 



"Statistics from Lincoln College, Canterbury, and Roseworthy 

 College, South Australia, are given in Table XII., and they 

 support the general conclusions arrived afr here. 



