[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 changing.* 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 extent 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 affections 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
[Footnote] * “The Population of New Zealand” (Trans. N.Z. Inst., vol. xxxiii., p. 453).
properly comparing the statistics of the same country for different years—that is, the difference in the age-distribution of the population—makes it necessary also in comparing the statistics of one country with those of another. Unfortunately, the necessary data for dealing in this manner with the statistics of any other country are not available in Auckland, and the work, therefore, cannot be attempted, though the results to which it would lead would be, I believe, of supreme interest.