144 THE TREND OF THE RACE 



creasing mortality. If people live longer, there is naturally a 

 larger number of them alive at any given time. If each family 

 always produced the same number of children the relative num- 

 ber of births per thousand would decrease as the number of 

 people alive at any given time increased. Therefore, with the 

 same marriage rate and the same degree of fecundity, a commu- 

 nity with a decreasing mortality would show a decreasing birth 

 rate, were we to measure birth rates, as is usually done, by the 

 annual number of births per thousand inhabitants. 



Marriage rates estimated, as they commonly are, by the num- 

 ber of marriages made annually per thousand of the population, 

 would be changed by both the birth rate and the death rate. 

 With a given number of marriages per annum, the rate per 

 thousand of the population would decrease with an increased 

 birth rate and increase with an increased death rate. In consid- 

 ering the relation of marriage, birth and death rates it must be 

 borne in mind that each of these affects the others as expressed by 

 the method usually employed. 



Changes in the birth rate arising from variations in the rate 

 and age of marriage and the death rate may be partly avoided 

 by employing the so-called ''corrected births rates" in which 

 allowance is made for changes in these factors according to the 

 method employed by Newsholme and Stevenson or some similar 

 mode of procedure. An index of birth rates for many purposes 

 more satisfactory is afforded by the number of children born 

 armually to every looo women of child-bearing age. What 

 method of enumeration is the best depends on the particular use 

 one wishes to make of the data. 



Statistics on the birth rate may also be vitiated to a certain 

 degree by immigration and emigration. In the United States, 

 not only foreign immigration, but the frequent emigration of our 

 people from one state to another introduces a source of error into 

 the statistics compiled by the several states. In addition, the 

 vital statistics of our states suffer from other sources of inaccu- 

 racy due to the way in which they are compiled. Data on births 

 are faulty owing to incomplete birth registration. Only a few 



