Definitions for "dependency ratio"
A measure of the portion of a population which is composed of dependents (people...
ratio of (potentially) economically active population to the retired population and children under 16 years of age. Aged dependency ratio is the ratio of the economically active to the retired population.
the number of people below age 15 and above 65 years of age expressed as a percentage of those aged 15 to 65 (working age)
Keywords:  divided, over
(Under 18 and Over 64) divided by (18 to 64).