demography -n. the study of changes (such as the number of births, deaths, marriages, and illnesses) that occur over a period of time in human populations

median – adj. the middle value in a series of values arranged from smallest to largest

advantage -n. something (such as a good position or condition) that helps to make someone or something better or more likely to succeed than others

evaporate –v. to go away suddenly, to disappear or vanish

exodus –n. a situation in which many people leave a place at the same time — usually singular