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10
population did not include persons resident in poor law institutions belonging to the district but
situated beyond its limits. If such persons were included in the population the "factors for
correction " would in some instances be slightly modified.
London mortality in the four years 1891-4 compared with the decennium 1881-90.
A valuable application of the Manchester Life tables in a comparison of the mortality in
Manchester in 1891-3 with that of 1881-90, is shown in a recent report on the Health of Greater
Manchester, 1891-3, by Dr. Tatham, the late medical officer of health.
In my last annual report a life table based on the mortality figures for London in the decade
1881-90 was published ; it is now, therefore, possible by means of this life table to institute a similar
comparison of the London mortality in the four years 1891-4 and that of the decade 1881-90.
The mean death rates in London at the several age periods in 1881-90 and 1891-4 are shown in
the following table—
Age period.
males.
Females.
Mean death rate
1881-90.
Mean death rate
1891-94.
Difference per
cent.
Mean death rate
1881-90.
Mean death rate
1891-94.
Difference per
cent.
0—
73.09
70.87
— 3.0
63.26
60.96
— 3.6
5—
5.93
5.46
7.9
5.-82
5.72
1.7
10—
2.92
2.63
— 9.9
2.89
2.66
— 8.0
15—
4.05
3.90
— 3.7
3.58
3.32
— 7.3
20—
5.44
5.06
— 7.0
4.40
4.01
— 8.9
25—
8.65
8.08
— 6.6
6.82
6.33
— 7.2
35—
14.96
15.23
+ 1.8
11.42
11.41
— 0.1
45—
23.87
24.61
+ 3.1
17.23
17.53
+ 1.7
55—
41.33
43.15
+ 4.4
30.77
32.44
+ 5.4
65—
77.97
80.58
+ 3.3
63.28
65.80
+ 4.0
75—
155.93
156.05
+ 0.1
134.28
136.60
+ 1.7
85 and upwards
297.63
288.41
— 3.1
264.77
260.67
— 1.5
All ages
22.10
21.53
— 2.6
18.83
18.46
— 2.0
It will thus be seen that whereas the mortality of males and females at all ages has declined in
the period 1891-4, that of males aged 35-85 and of females aged 45-85 has actually increased, the
decline in the death-rate at "all ages" being almost exclusively due to a decline in mortality at the
early age periods.
These figures do not give more than an approximate indication of the nett gain or loss to the
community, and it is in arriving at a more accurate result in this respect that a life table is especially
useful. The following example of an extreme case may show this more clearly.
Assume that in a certain community 800 deaths occur in one year, and that 400 of these deaths
occur among persons aged 0-25, whose mean future lifetime is, say, 30 years, and that the remaining
400 deaths occur among persons aged 25 and upwards, whose mean future lifetime is, say, 15 years,
then these 800 deaths will represent a total of 18,000 years of " life capital" lost to the community, for—
(400 X 30) + (400 X 15)= 18,000.
Now suppose that 700 deaths occur in the same community in the following year, and that 600 of
these deaths occur among persons aged 0-25, and the remaining 100 among persons aged 25 and
upwards, then the loss of life capital to the community will be (600 X 30) + (100 X 15) = 19,500
years. Thus, while there is a saving of 100 lives in the second year compared with the first, there is an
actual loss to the community of 1,500 years of " life capital."
It is therefore apparent that the actual number of lives saved in any period is an unreliable
measure of progress, and that the value of each life gained or lost must be considered in order to arrive
at more accurate conclusions.
The following table shows the mean future lifetime of males and females in certain groups of
ages. These figures have been calculated* from the figures in the Ex and Qx columns of the life
table for London, 1881-90, published in my last annual report.
* The future lifetime of lx persons is Qx, and the mean expectation of life of each of these persons is Qx/lx The future lifetime of Px
persons living at all ages between x and x + 1 is Qx- Px/2, the mean expectation of life of each being Qx/ Px-½. The future lifetime of
Px + Px + 1 + Px + n _ 1 persons living at all ages between x and z + n is
and their mean expectation of life equals-
This formula ha9 been used for the age group 0—5 years, Px being taken as the geometrical mean of lx and lx + i, i.t.
except in the case of the age period 0—1 ; in this case the mean number living at all ages between 0 and
1 has been deduced from the recorded proportion of deaths under 3 months, 3 months to 6 months, and 6 months and under montns.
In the case of the age period 5—10. the mean expectation of life has been assumed to equal the arithmetical mean of the expectations
of life at the precise ages 5 and 10, and similarly in the case of succeeding age periods.