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105
Report of the County Medical Officer—General.
III. The London Life Table, 1901-1910.
Method of
construction.
It has long been recognised that crude death-rates afford an inadequate and fallacious basis
for the purpose of comparing the health conditions of different communities or of the same community
at different periods of time. The use of a life table for comparative purposes of this nature is more
free from objection inasmuch as by this means errors due to differences in the age and sex constitution
of the populations compared are eliminated, and to this extent the reliability of comparative result is
increased. The large amount of arithmetical labour involved in the preparation of an extended life
table militates against the general use of this method of comparison. Notwithstanding this, however,
an increasing number of extended decennial life tables for large urban communities have been constructed
in recent years.
The first extended life table for London was published as an appendix to the Report of the County
Medical Officer of Health and was based on the mortality experience of the decade 1891-1900. In the
introduction to that table the Medical Officer stated: "This table is, it may be hoped, the first of a series
which will enable comparison to be made between the viability of the London population in successive
decennia, and thus show whether there is indication of progress or of regress, and whether the movement
in either direction corresponds with the changes observed in other parts of the country." The present
table is the second of the series and its value is enhanced by the fact that the results can be compared
with those obtained by the construction of the first life table. The method of construction
followed is generally the same as that used for the life-table of 1891-1900, described in detail
in the annual report of the Medical Officer of Health of London for the year 1901,
Appendix I., in which will be found the first London life-table. A different method of calculating
the mean intercensal population was required for the present life-table, as it was
apparent that the population of the county was increasing at the time of the 1901 census
and subsequently began to decline, so that there was a net decrease of 14,582 persons during
the ten years intervening between the census of 1901 and that of 1911. The assumption that the
population had increased in geometrical progression, which was reasonably made in the previous decennium,
could not in the circumstances be made here; and it was therefore decided to calculate the intercensal
population in the period 1901-1910 from the censuses of 1891, 1896, 1901 and 1911 by integrating
between suitable limits the difference equation of a population curve deduced from these four census
populations. Reference may be made on this point to London Statistics, Vol. XXII., p. 32, where the
results of various methods of arriving at the intercensal population are presented in diagrammatic
form. With regard to the calculation of the age-group populations by sexes, only three censuses could
be used, as ages were not enumerated in 1896. The aggregate of the age-group populations thus determined
somewhat exceeded the total mean population derived from the four censuses, and it was therefore
necessary to reduce each age-group population proportionately.
Circumstances
affecting
the estimate
of the mean
intercensal
population.

(a) Slight alterations in the county boundary between 1891 and 1911 affecting the populations shown only to
a negligible extent have been ignored, but the addition of South Hornsey to the county area in 1901 has been allowed
for by the inclusion of the census population of that area throughout.
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