As indicated above a "net" birth rate is used , mainly because an actual birth rate cannot be calculated form the UN data , and considerable work would be involved in gathering data an actual birth rates for all countries.

Use of "net" birth rate will however not affect the long term predictions. The lower birth and death rates will cancel each other out. The effect of the use of "net" birth rates are :

            1) "Net" birth rate is lower than the actual birth rate.
            2) The exclusion of infant deaths (0-5) will also mean a lower death rate.