Definition
Composition of an aggregate that remains unchanged throughout the entire time series of a statistic, regardless of whether its definition has changed over time.
Further information
The composition of an aggregate (of financial instruments, institutional sectors, or political or economic regions, for example) can be altered by economic changes, regulations, or statistical needs, among others. In this case, it is necessary to define and specify the exact composition considered in each observation of a statistical series.
In these situations, one of the following two criteria is usually applied when estimating the statistical series:
- it is considered that throughout the entire time period, the composition was the same as the current or most recent one
- it is considered that in each observation, the aggregate is formed by the definition applied at that time
In the first case, what is known as a ‘fixed composition’ is used, while in the second case, a ‘changing composition’ is applied.
Let’s consider, for example, the statistical series of the euro area population. This series with a fixed composition would offer the aggregated data of all the countries that make up the area in its most current formation. However, the series with a changing composition would not take into account the data of Croatia for observations prior to January 2023, as that country did not join the area until that date.
Related concepts
Update date: January 2025
