More on population projections

We stated in our earlier post on population projections that they are conditional and based on assumptions. These assumptions form the basis of predictions of what changes will occur in the population size and structure. 

It is critical to involve multiple stakeholders and experts in the determination of these assumptions because it allows for:

•       A thorough assessment of existing trends.

•       Identification of potential changes (political, economic, health, legal etc.) that can impact population trends going forward

•       Knowledge of subgroup trends that are not yet obvious at the population level (e.g. antenatal coverage increasing in remote rural areas)          

What are population projections?

Population projections are generally an estimate of what the population will look like in future. 

More specifically, projections are an educated guess of the population size and structure based on assumptions about future population trends and analyses of current and historical trends. Population projections are conditional and the resulting figures are dependent on the underlying assumptions.

Total Fertility Rates

The standard measure of fertility is the Total Fertility Rate (TFR).

Total Fertility Rate is the number of children than a woman has. TFR ranges from 1 in South Korea to 6.9 in Niger (2018 World Bank est.) with the top 25 highest fertility countries in sub-Saharan Africa, mainly from West and Central Africa.

Replacement level fertility is the level of fertility required for each generation to replace itself. Normally, 2 people would need to have 2 children to replace themselves. However at the population level the replacement TFR would have to be greater than 2 to account for the loss of children who will die before reaching adulthood. Replacement level TFR is thus considered to be 2.1 (in high mortality settings however, replacement level fertility would have to be higher because a greater proportion of children die in childhood).

Basic fertility concepts

Fertility, one of the population processes is defined as the number of children born to a woman. 

What is known as fertility (i.e. the physical ability to have children) in conventional language is referred to as fecundity by demographers.

Fertility is determined by two main factors - biological and behavioural. The behavioural factors exert a greater influence on fertility than the social factors. 

How to measure population change

Today we continue our introduction to basic population concepts by reviewing how to measure population change.

Population change over time can be measured in the following ways:

• Natural increase = (Live Births) – (Deaths)
• Net migration = (Immigration) – (Emigration)
• Population growth = (Natural increase) + (Net migration)

All the indicators of population change can be:

• Positive (population size is increasing)
• Zero (population size is not changing)
• Negative (population size is declining)

What are population processes?

World Population Day is on July 11th so we will spend the lead up to the day highlighting some basic concepts in the field of population. 

Today we start with population processes.

Population processes are the three factors that lead to changes in the size and composition of the population. These are fertility, mortality, and migration.