A measure of the portion of the population that is composed of dependents, people who are too young or old to work. The dependency ratio is calculated by dividing the number of individuals aged below 15 or above 64 divided by the number of individuals aged 15 to 64. A rising dependency ratio is a concern in many countries that are facing an aging population, because it is difficult for pension and social security systems to provide for an older, non-working population.