Segaii. — On New Zealand Health Statistics. 115 



Art. VII. — On the Becent Statistics of Insanity., Cancer, 

 and Phthisis in Neiv Zealand. 



By H. W. Sbgar, M.A., Professor of Mathematics, University 



College, Auckland. 



Plates II.-IV. 



[Read before the Auckland Institute, 2nd September, 1901.] 



I have previously pointed out the rapid way in which the 

 age-distribution of the population of New Zealand is chang- 

 ing.* Because of this rapidity of change in the population, 

 numbers giving the proportion which those subject to any 

 disease or infirmity bear to the whole population at different 

 times are of little or no service for purposes of comparison 

 unless the people of all ages are about equally subject to the 

 complaint. If people of certain ages have more than the 

 average liability to the disease, an increase in the proportion 

 which the number of people of those ages bears to the whole 

 population must tend to increase the proportion of the 

 population subject to that particular affliction. 



It follows that, for the proper investigation of the progress 

 of any affection during any period, we must consider the ex- 

 tent to which each section of the people of about the same 

 age has been affected by it during the period. This work I 

 have carried out for insanity, cancer, and phthisis, three affec- 

 tions which, as they afflict severally a greater number of the 

 human race than almost any other single disease, are likewise 

 more the objects of popular interest than any others. With 

 respect to each of them I have taken, for each sex and for 

 various age-periods, the statistics for each year from 1879 

 to 1898, and have grouped them in five-year periods, each 

 having a census year as the central year. I have then taken 

 the averages for each period of five years and compared them 

 with the populations of the same sex included in the various 

 age-periods at the corresponding censuses.' The results are, I 

 think, of considerable interest, and will be described in the 

 following sections. 



There is no attempt made to institute comparisons with 

 other countries. Such comparisons are of little value unless 

 the statistics of each country are treated in some such way as 

 that I have used in treating New Zealand; for' the same 

 reason that makes this method of treatment necessary in 



* " The Population of New Zealand " (Trans. N.Z. Inst., vol. xxxiii 

 p. 453). 



