THE FALL OF THE BIRTH-RATE 17 



called the " indirect " method of standardisation. We 

 take any data that may be available from any source 

 whatever giving the numbers of births per thousand 

 married women at successive age-groups, hoping, 

 ever, that even if they represent a rather higher 

 or lower average fertility the form of the law (the 

 change in fertility with age) is approximately the same 

 as for our own women. We then apply these arbi- 

 trarily chosen fertility rates to the populations of 

 married women at each successive census and thus 

 calculate the birth-rate there would have been (rec- 

 koned on the total population) if our married women 

 had exhibited the standard fertilities. These "poten- 

 tial" or "index" birth-rates are simply measures of 

 the favourableness or otherwise of the constitution 

 of the population for the production of children. 

 Taking some fixed year as the standard year of refer- 

 ence, the ratio 



index birth-rate in standard \\-.\r 

 index birth-rate in any other yea r 



gives a factor for the correction or standardisation of 



the birth-rate in that other year. For if the index 



birth-rate in that other year is low compared with 



the index birth-rate in the standard year, its popula- 



must have been unfavourably constituted for the 



production of children there must have been few 



married women in the population, or they must have 



been relatively old and to correct for this we must 



have to multiply by a factor greater than unity, as 



above. Conversely, ndex birth- i<jh,the 



population is favourably constituted and the eofl 



or standard ctor must be less than unity. 



rocess of c< -\ (as it used to be term. 



lardisation (to use the modern phrase) was 



first discussed and applied by Dr Newsholmc (now 



19 



