One frequently used index for globally summarizi ng age distributions is the dependency ratio, or  the ratio of the dependent-age population (young  or old) to the working age population. The  higher this ratio is, the greater  the burden of support on worki ng people in specific geographic  areas. In general, researchers have used depende ncy ratios to consider  whether a population is  “too young” or “too old.” Much has been made, for ex ample, of high fertility  rates in Africa and  the forecasted “age bubble” predicted for China (U nited Nations World Population Prospects,  2006), where ratios of nearly one dependent for  each person of working age have been either  observed or predicted.