What evaluation techniques are used for population projections?

Population projections are evaluated using techniques such as cohort-component methods, trend extrapolation, and mathematical modelling.

The cohort-component method is a commonly used technique for population projections. It involves dividing the population into cohorts, or groups, based on age and sex, and then projecting each cohort separately. The projections are based on assumptions about future fertility, mortality, and migration rates. This method is particularly useful for long-term projections and for understanding the demographic processes that drive population change. However, it requires detailed data and assumptions about future trends, which can be difficult to obtain and may not always be accurate.

Trend extrapolation is another technique used for population projections. This method involves identifying trends in historical data and then extrapolating these trends into the future. This can be done using simple linear extrapolation, or more complex statistical methods such as time series analysis. Trend extrapolation is relatively simple and quick to implement, but it assumes that past trends will continue unchanged into the future, which may not always be the case.

Mathematical modelling is a more complex technique used for population projections. This involves developing a mathematical model that describes the relationships between different demographic variables, such as birth rates, death rates, and migration rates. The model is then used to project future population changes. This method can be very accurate, but it requires a high level of statistical expertise and computational resources.

In addition to these techniques, population projections can also be evaluated using expert judgement. This involves asking experts to make predictions about future population trends based on their knowledge and experience. This method can be useful for incorporating qualitative information and for dealing with uncertainty, but it is subjective and can be influenced by the experts' personal biases.

Overall, the choice of evaluation technique for population projections depends on the available data, the time horizon of the projection, and the level of detail required. Each technique has its strengths and weaknesses, and often a combination of techniques is used to provide a more robust projection.