Uses and Limitations of Population Projections

Uses of population projections
It is important to have high quality statistics on the population and projections of the population, for policy development and for planning and providing public services. Their uses include:

• central and local finance allocation;
• informing local and national policy;
• childcare and schools planning;
• housing and land use planning;
• health care planning;
• modelling and projecting health care indicators;
• weighting surveys;
• benchmarking other projections and as a control for smaller area projections;
• looking at the implications of an ageing population;
• making national and international comparisons.

 
Strengths and limitations
Population projections have limitations. A projection is a calculation showing what happens if particular assumptions are made. The population projections are trend-based. They are, therefore, not policy-based forecasts of what the government expects to happen. Many social and economic factors influence population change, including policies adopted by both central and local government. The relationships between the various factors are complex and largely unknown.

The reliability of projections decreases over time, and projections tend to be less reliable in periods of rapid change. Projections for areas with small populations tend to be less reliable than those for areas with large populations. Projections of the number of adults (particularly elderly people) are usually more reliable than those for children because they are based on people who are already living in Scotland. Migration tends to fluctuate more than fertility or mortality, and it is harder to measure, so there tends to be more uncertainty around the migration figures.

Each publication compares the most recent set of projections to the previous ones.

Consequences of projections
Population projections, like some other types of projections, may indicate that existing trends and policies are likely to lead to outcomes which are judged undesirable. If new policies are then introduced, they may result in the original projections not being realised. However, this means the projections will have fulfilled one of their prime functions, to show the consequences of present demographic trends with sufficient notice for any necessary action to be taken.

Development plans may be based on reasoned and agreed departures from the projections if they seem better placed to fit particular local circumstances.

Variant projections
Variant projections were not produced for the 2020-based interim projections. Usually they are produced to give users further information on the projected populations of Scottish areas, and to give an indication of the inherent uncertainty of demographic behaviour, especially for long-term projections. The variants allow users to consider the impact upon the demand and supply of services, such as education, health, and care of the elderly, if future fertility, mortality and migration differ from the assumptions made for the principal projections. They are not intended to represent upper or lower limits but to illustrate plausible alternative scenarios of future demographic behaviour.