This has a major influence on survival rate. Across the world, adults are generally surviving to live to an older age as well. Modern medicine has also made a significant contribution to people living longer. As a method to understand reasons for population growth, geographers can compose a population pyramid, to examine the age-sex structure of a country. This compares the male population to the female population in different age groups.
Geographers also look at demographic transition models.
These are multi-stage models based on Western Europe's experience of changes in population growth as countries undergo industrialization. There are four distinct stages to the model. The first stage is called high stationary, and is characterized by both high birth and high death rates. Currently there are no countries in this category. The next stage is known as the early expanding stage, which is characterized, by high birth rates and low death rates.