Calculations on an international scale

The most notable assessments involving several countries at one time are those made by the Population Division of the UN Organization on a worldwide basis. The methods adopted are necessarily those appropriate to countries with limited demographic data, for a more refined approach would be possible for only a relatively small part of the population of the globe. The first projections, made quite early in the history of the Organization, were on a relatively simple basis of extrapolation of curves representing crude birth rates and death rates for groups of regions. In a second approach, the same system was carried out in greater detail as to area, but in a third assessment the method employed was one of population models. Particulars of the method of calculation in the fourth and most elaborate exercise are not available, but still closer attention than before was devoted to the individual circumstances of sub-regions and countries. The results of these projections are discussed in chapter 14 above. Simplified methods of projection have also been devised by the UN Population Commission for the use of relatively unskilled staff in under-developed and partly-developed countries. The principal elements of the methods are (a) a standard series of model life tables by means of which future improvements in longevity could be estimated, and (b) a discussion of methods of appraisal and correction of incomplete and inaccurate birth and death registration data.

Series of population projections are sometimes made for several countries at the same time.