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might have succumbed to infection locally but, before diagnosis
is made, have removed from the district. (6) The age incidence
of the population is abnormal and influences the crude notification
rates. Standardization would eliminate this, were there no
other deficiencies in notification rates in general.
The number on the register.-This as a measure of comparison
is subject to most, though not to all, of the deficiencies of the notification
rate.
Standardizing the death rate or making a comparison of deaths
per thousand in different age-groups removes the variations due to
abnormal age distribution. This method however is still subject
to the disadvantages that the deaths were not necessarily those of
persons who contracted the disease locally. Merely to ignore those
cases who are diagnosed as tuberculous before transfer is not
sufficient ; many cases have been notified for the first time within
a few weeks of coming to reside here, most of these obviously having
been infected elsewhere. To take the time as dat ing from the onset
of symptoms and not from the date of notification is still not
sufficient; some gave the date of onset of symptoms within a few
weeks of residence in this locality. The problem is, what period of
time to allow for the effect of residence elsewhere. If residence
on the estate is beneficial, up to what period of time does one
assume that the previous adverse influence is operative. On the
other hand, if residence here is baneful, how long a period must
one assume local residence is necessary to overcome the previously
healthy state of the body. Another fallacy of comparison of
death rates is that found to occur in the case of notifications,
namely, that tuberculosis might be contracted here but the
person removes from the district before death.
These then, are some of the difficulties which prevent an
answer being given at the moment from consideration of this
estate to any question as to the influence of housing on the
tuberculous.
Certain of these difficulties have been overcome in various
ways, and the following figures are given as an indication of the
trend of the course of the disease:—
Notification Rate.—To remove any question of transferred
population or of the disease having been acquired before trandgr,
only those cases are considered in which the onset of symptoms
occurred over 6 months from the time the patient first resided
here. Six months is an arbitrary figure and a longer period
could be defended. On the other hand, it did form a convenient
line of demarkation as most of those who did not fall within the
6 months gave a period of over 12 months, there being very few