Which of the following is NOT one of the three demographic variables that change the size of a population?

• A. Fertility
• B. Net migration
• C. Population growth
• D. Mortality

Answer: (C)

Think of how a population changes as coming from three main forces: births, deaths, and movement of people. Fertility measures how many babies are born and thus adds to the population. Mortality measures how many people die and thus reduces the population. Net migration captures the balance of people moving into and out of the population, which can increase or decrease size depending on the direction. Population growth, on the other hand, is the overall change in population over a period as a result of those three processes. It’s not a separate driver itself; it’s the outcome created by fertility, mortality, and net migration. So the option that isn’t one of the three variables is population growth.