Statistical Language - Estimate and Projection
Estimate and Projection
What is a projection?
A projection indicates what the future changes in a population would be if the assumptions about future trends actually occur. These assumptions are often based on patterns of change which have previously occurred.
For example: Data collected about the total number of store locations for a retail chain over three years show an increase from 8 stores in first year, to 12 stores in the second year, to 18 stores in the third year. It could therefore be projected that if the chain continues to expand following the same pattern of increasing by half (50%) each year there will be 27 stores after the fourth year.
A projection is not making a prediction or forecast about what is going to happen, it is indicating what would happen if the assumptions which underpin the projection actually occur.
Comparison of Projections and Forecasts
How do estimates and projections differ?
An estimate is a statistic about a whole population for a previous reference period which is based on data from a sample of the population, whereas a projection is a statistic indicating what a value would be if the assumptions about future trends hold true (often drawing upon past movements in a population as a guide for the assumptions).
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3222.0 - Population Projections, Australia, 2006 to 2101
3228.0.55.001 - Population Estimates: Concepts, Sources and Methods