A manual of public health / by A. Wynter Blyth.

  • Blyth, Alexander Wynter, 1844-1921.
Date:
1890
Catalogue details

Licence: Public Domain Mark

Credit: A manual of public health / by A. Wynter Blyth. Source: Wellcome Collection.

    44/775 (page 15)
    I] Factors (reciprocals)1 will in all these cases be found most convenient, and the factor need seldom be more than three figures. For instance, the month of 28 days gives a factor for All Souls, in the writer's district, of '4879, and supposing in the month there are 56 births, then 56 x '4879 = birth-rate 27*32, but the same result is obtained by multiplying by 488; similarly a factor of •8909 may be transformed into 891, or a factor of '561 may even be made into two figures, viz. -56, without introducing inaccuracy of great moment.'2 In the same way the daily population may be converted into the population for a quarter by multiplying by either 90 or 92 as the case may be ; but the error in taking three months as exactly a quarter of a year, is immaterial, and rates may for this purpose be calculated by simply multiplying the births or deaths by 4 x 1000, and dividing by the population. (9) Age Distribution. A rate derived from a population of every age from the newly- born to the limit of human existence gives but scanty information. The normal death-rate below 5 is something like 66 per 1000, between 10 and 15 it sinks to 5, persons over 85 die at the rate of 294 per 1000; it is therefore evident that should a district from the presence of institutions for the aged or the very young have a number of the less vital members of the community in excess of other districts, the death-rate will be large ; but such a rate, unless beyond or below the normal rates for those age-periods, affords 1 A table of reciprocals of numbers from 1 to 100,000, with tbeir differences, by wbicb the reciprocals of numbers may be obtained up to 10,000,000, by Lieut.-Col. W. H. Oakes, is published by Messrs. C. and E. Layton, London, and will be found most useful. 2 Mr. Sydney Lupton writing in Nature observes :— It is convenient to bear in mind the following simple rules, due I believe to De Morgan. If two numbers, a and b, each true to the first decimal place, are multiplied together, the result is true to a only ; a second true decimal in each number makes the result ten times more correct, and so on. In dividing ^ where each is true to the first place, the result is true to ^ * ^ , and so on. Any attempt at greater accuracy in cal- culation than is indicated by these results should be avoided, since it only precludes the use of cheap and handy tables, tires the calculator, making him more liable to error in the important figures, and tends to give a false idea of the accuracy of the experiments on which the calculations are based.