Key Terms Replacement Rate: a fertility rate of 2.1. Two children per family are required to replace each parent. The .1 is needed to overcome the deaths of some children. Dependency Ratio: population ratio based on age that describes those too young or too old to be in the work force. Case Study: Japan Population Density and Aging Population Videos Japan Population Infographic Train Stuffing Tokyo Wave Pool Capsule Hotels Case Study: Germany Negative Population Growth Germany's Demographic Decline Case Study: China One Child Policy Suffering Caused by China's One Child Policy