Segar. — Insanity: Some Comparative Statistics. 223 



(1) liability to insanity were independent of age once the age of twenty is 

 reached, and as if (2) the age-distribution for ages above twenty were the same 

 for both the native-born and immigrant populations. Now, this is very far 

 from being the case in either particular. For instance, at the ages 20-25 

 there are only 13-32 lunatics to 10,000 of population ; at 65-70 there are 

 133-34, an increase in the ratio of 1 to 10 ; and the increase is steady from 

 the one age-period to the other. Again, in the former of these age-periods 

 the native-born population is more than five times the not-native-born ; in 

 the latter it is less than one-seventieth ; and again there is a steady change 

 from the one position to the other in between the two age-periods. Fig. 1 

 represents by graphs the age-distribution of the whole population and also 

 that of the native-born. It represents also the lunacy-rate — that is, the 

 number of lunatics to 10,000 of population at each age-period. The diagram 

 shows clearly how, as the lunacy-rate increases, the ratio of the native-born 

 to the whole population of the same age-period becomes less and less, until 

 by the time the lunacy-rate has reached its maximum this ratio is very 

 small. Consequently, in the two populations of over twenty, the native-born 

 are to a far greater degree than the others concentrated in the earlier age- 

 periods, in which the liability to lunacy is much smaller than in the later 

 ones, and consequently the number of native-born lunatics is to be expected 

 to be very much less than it would be if with the same populations these 

 differences did not exist. We have further to allow for the population not 

 New-Zealand-born containing a large majority of males, with their greater 

 liability to insanity. 



In Table I, I have made an attempt to allow for these differences. The 

 table gives the whole population and then the native-born population in 

 quinquennial age-periods. The fourth and fifth columns give the latter 

 divided into males and females. The next two columns give the number 

 of lunatics per 10,000 of population for each age-period. On the hypo- 

 thesis of equal liability to lunacy at the same ages in both classes of popu- 

 lation it is now a simple matter to calculate the proper number of native- 

 born lunatics of each sex in each period. The results are entered in the last 

 two columns. 



This method, it should be noted, still exaggerates the estimate of the 

 number there ought to be of native-born lunatics if they had the same liability 

 to insanity as the remainder of the population. For the condition of things 

 we are trying to allow for still holds for each of our age-periods. The pro- 

 portion that is native-born is greater in the earlier than in the later years 

 of each age-period, and uj) to about seventy years the liability to lunacy is 

 continually on the increase as the age increases, while after this age the 

 contribution to the number of lunatics is small by reason of the smallness 

 of population. It is impossible to allow for this feature with perfect accu- 

 racy. If we took yearly age-periods the error would be smaller, but the 

 problem is hardly worth this, and it is sufficient for our purposes that it 

 should be clearly understood that the estimate in the table is distinctly an 

 overestimate. The figures in the table are all taken from or based on the 

 census returns for 29th April, 1906. The lunacy-rates quoted here and 

 elsewhere are those for New Zealand as determined by this census, but their 

 general character is in no way peculiar. Their main feature is general — 

 namely, an increase in the rate up to sixty-five or seventy years of age, after 

 which there is a not very great reduction, due to the greater mortality of 

 he insane causing a reduction in their relative numbers. 



