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30
the low total rate of the year. An excessive prevalence for
the first two months for 1930, when for eight consecutive
weeks double figures were recorded, brings up the total incidence
from the beginning of the Autumnal rise to the anticipated
figure. That is to say that, had these excess cases occurred
at the end of 1929 instead of at the beginning of 1930, the
Diphtheria rate for the District would have shown, just as
he Scarlet Fever rate showed, a slight excess over that obtaining
in the country as a whole.
The interesting features of these figures is shown by com-:
parison with the preceding years. For Scarlct Fever the factor
of incidcnce in Dagenham, compared with the country as a
whole for 1927 was 1.6,. for 1928 1.4 and 1929 1.1. The corresponding
figures for Diphtheria were 1.7, 1.3 and 0.9.
Considering the cases occurring in the Estate houses alone,
the expected incidence of Scarlet Fever,(all cases) was 344, compared
with an actual incidcnce of primary cases only of 351.
For Diphtheria there were 189 primary cases on the Estate
compared with an expected number of 178 all cases. The
expected rate is calculated from the number of houses and the
population per house, allowance being made for the altered
age distribution of the population.
Plotting these figures on the graphs of actual and expected
incidence, it is seem that the lines of the curves vary.
For Scarlet Fever the incidence curve remained low until 1925,
when it underwent a marked alteration in direction, so that in
1927 it crosscd the curve representing anticipated cases and
fame to lie above it. Since that date both curves have converged
and arc now running parallel and almost coincident,
since the expected and actual figures for 1929 and 1928 were
almost equal. In spite of the deceleration in the rate of housing
growth, these two curves for Scarlet Fever continue in the
same line as for previous years and do not run parallel to the
Population curve.
. The Diphtheria curves up to this year remained essentially
similar to the Scarlet Fever curves, except that the marked
change in the direction of the incidence curve took place a year
later in this disease in 1927 the incidence crossed the
anticipated curve and rose well above it for 1928. In 1929. however
the two curves converged again, the actual number of cases
being only slightly more than the expected incidence. Fur-
ther the curve of actual incidence, instead of continuing in a