when the whole duration of life from birth to death is included in the calculation. This is only true for a stationary or life-table population, in which the number dying is assumed to be regularly replaced by a corresponding number of persons of the same age.
Life Capital.—The life-tables now in use are those based on the experience of 1881-90. The gain in any subsequent year, as in 1900, may be ascertained as follows: the mean population and the death-rate for each age-group as 0-5, 5-10, etc., are calculated. Then the mean death-rate of the same community for 1881-90 is applied to this population. By this means the “calculated number” of deaths in 1900 is obtained. The difference between these numbers and the “actual number” obtained from the death-registers, gives the gain or loss during the year. Next multiply these differences by the mean expectation of life for the corresponding groups of years. By adding the gains thus ascertained and subtracting any losses, we obtain the net gain in “life-capital” (Tatham) during the year 1900.
Tests of the Health of a Community. 1. The general death-rate is the test most commonly applied, and generally trusted. It has its limitations in this respect. It may usually be trusted in comparing a town or district for a single year with preceding years, as the age and sex distribution of a given population only changes slowly. But when comparison with other towns or districts is made, the possibility that erroneous conclusions may be drawn becomes considerable. (a) Before the death-rates of two districts can be compared, either this comparison must be made by means of death-rates for age-groups (0-5, 5-10, ... 65-75, etc.) or the factors of correction, the method of obtaining which is described on page [341], must be applied. (b) It must be ensured that in the two compared districts, an equal amount of correction has been made for deaths occurring in public institutions and among visitors (page [340]). (c) Even when the above precautions are taken, it is conceivable that a town with a death-rate of 15 per 1,000 may really be as healthy as another with a death-rate of 12 per 1,000, though a statistical justification of this statement is a difficult task.
Social conditions quite irrespective of the sanitary condition or the natural salubrity of a district have an important influence on the death-rate. Poverty and all that it connotes, necessarily involves a higher death-rate than occurs among the well-to-do. Furthermore, the domestic servants employed by the latter frequently die in districts other than those in which they are employed, without any possibility of the requisite correction being made.
2. The zymotic death-rate is frequently quoted as a test of sanitary condition. This is a death-rate based on the deaths from the “seven chief zymotic diseases,” small-pox, measles, whooping-cough, diphtheria, scarlet fever, fever (chiefly enteric), and diarrhœa. This death-rate should be entirely discarded, the death-rate from each infectious disease being separately stated. A high death-rate from enteric fever would be a much more serious reflection on the health of a town than a high death-rate for whooping-cough.
The death-rate from each of these diseases in London and in England in 1899 was as follows:—
DEATH-RATE IN 1899 PER 1,000 LIVING.
| England and Wales. | London. | |
| Small-pox | ·005 | nil |
| Measles | ·32 | ·47 |
| Scarlet fever | ·12 | ·08 |
| Diphtheria | ·29 | ·43 |
| Typhus | ·001 | nil |
| Enteric fever | ·20 | ·18 |
| Whooping cough | ·32 | ·38 |
| Diarrhœa | ·94 | ·92 |
A statement of the death-rate from each of these diseases for a series of years is a much more trustworthy test than a similar statement for a single year, in which accidental causes may have caused a temporary increase, or than a statement of the average result for a series of years, which tends to conceal the epidemic variations of the disease in question. The danger of such averages has been well exposed by Chadwick in the remark that “a mean between the condition of Dives and Lazarus tends to make it appear that after all Lazarus has not so much to complain of.”
3. The infantile mortality (page [342]) is a delicate test of mixed sanitary and social conditions, and stress may always be laid on it from these standpoints. The importance of comparing death-rates at other age-groups has already been explained.