The broad age span from 15 to 64 years coincides approximately with that of full working capacity. A 'dependency ratio' can be calculated, relating numbers of the population with ages less than 15 or greater than 65 to 100 persons of these 'working ages'. The above figures signify a dependency ratio of 73% for the world, 57% for the more developed regions, and 81% for the less developed regions.
A sharp difference exists between the population compositions by age group in the more developed and the less developed regions. Because of generally low birth rates over decades in the past, the more developed regions have a much more moderate proportion of children than do the less developed regions, but the proportion of older persons (aged 65 years and over) is markedly greater in more developed than in less developed regions. It follows that the burdens of child rearing and education in the less developed regions will be proportionately much heavier if standards are to be reached comparable to those in more developed regions. So far these standards are not reached; children from the age of 9-10 years may take on almost full working responsibility, and before this age they may be working partially and contributing valuably to the family income. On the other hand, greater and still growing needs exist in more developed regions in the care of older persons, although working life or the possibility of working life may extend beyond the age at which social and commercial conditions generally tend to terminate it.