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10
accepted as valid comparative measures of the mortalities experienced
by the several populations.
" In practice, however, populations are not thus similarly
constituted and their crude death-rates fail as true comparative
mortality indexes in that their variations are not due to mortality
alone but arise also from differences in their population constitution,
the two elements being combined in indistinguishable
proportions. In order to isolate the mortality factor it. is first
necessary to identify and remove the population variable.
" One of the methods commonly adopted for this purpose is to
select a set of mortality sex-age rates as a standard and to ascertain
the hypothetical population death-rates yielded by applying the
standard mortality to the appropriate sex-age sections of the
populations under review; variations in the hypothetical deathrates
thus produced can only arise from differences in population
constitutions and they thus provide a means of assessing the extent
to which the ordinary crude death-rates should be modified in
order to provide a valid mortality comparison as between one
population and another.
" For the present purpose, the average mortality rates experienced
in England and Wales during the three years 1930/2 divided
into 11 sex-age groups have been adopted as the standard and
have been applied to the corresponding sex-age groups in the 1931'
census population of every Borough, Urban District and Rural
District in the country. The adjusting factor now supplied in
respect of a given area represents the ratio of the resulting deathrate
for the national 1931 census population to the similarly
obtained hypothetical death-rate for the said area. The factor
may be said to represent the population handicap to be applied to
the area and, when multiplied by the orude death-rate experienced
in the area, modifies the latter so as to make it comparable with
the crude death-rate for the country as a whole or with the
similarly adjusted death-rate for any other area. Strictly, the
adjusting factor applies only to death-rates experienced in the
year 1931 on which the several population handicaps have been
measured, but population constitutions change relatively slowly,
and save in exceptional circumstances, the 1931 factor may be used
for practical purposes until fresh population constitutions are
available from the next census."
The factor for Walthamstow is 1.11 which, applied to the
crude death-rate of 10.3 for 1934 yields an adjusted death-rate of
11.4 as against the figure of 11.8 for England and Wales.