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It will thus be seen that the death rate from whooping cough has increased from 2-45 in 1871 to 2 92 in 1881, this
increase being entirely due to the altered age constitution of the population. It follows, therefore, that the two rows of figures
obtained by taking the "all ages" death rate as 100 are not altogether trustworthy for purposes of comparison in the case of
6uch diseases as whooping cough and measles.
Throughout this report, however, the tables showing the increase or decrease per cent, at each age period have been mainly
used for purposes of comparison. It ie, however, interesting to observe the effect of the changes in the age constitution of the
population upon the comparative death rates, and for this purpose the following table has been prepared, in which the "all
ages " death rates used for each period have been approximately corrected for changes in the age constitution of the population
by the following method—
The recorded death rates at each age group for the periods 1851-60, 1861-70, 1871-80 and 1891-6 have been applied to the
mean populations of the period 1881-90, and a death rate at " all ages " has been calculated for each period from the numbers
of deaths thus obtained.
The corrected death rate at "all ages," therefore, for the period 1851-60, for example, represents the death rate at "all
ages" which would have obtained in 1851-60 hal the mean population of that perio I been similar as regards age constitution
to the mean population in 1881-90.