Factors influencing population change Populations change as a result of the balance between birth rates and death rates (known as “natural change”), as well as the movement of people from place to place (migration). The Demographic Transition Model This model/diagram summarises five stages that a country can pass through, in terms of its birth rates and death rates, as it develops socially and economically. As well as showing the changing patterns of these two variables, it also shows the resulting rate of population growth (or decline in stage 5).