bázisév

Bázisév, in statistical and economic contexts, is the base year used as the reference point for index numbers and time-series comparisons. It serves as the denominator against which values in other years are measured, allowing trends and relative changes to be expressed in comparable terms. In many statistical series, the base year value is normalized to a convenient number, commonly 100 or 1, so that changes over time can be read off as percentages.

Bázisév is typically fixed for a given series, although some indicators are periodically rebased to reflect new data or to keep the numbers interpretable as the base year becomes less representative due to long time spans. Rebasing does not alter real growth or inflation rates; it changes the numerical level to maintain a meaningful reference point.

The calculation is straightforward: index value in year t = (value in year t / value in base year) × 100 (or × 1).

Example: if the consumer price index uses 2015 as the base year, then CPI 2015 = 100. If prices rise such that the index is 110 in 2020, this indicates a 10% increase relative to 2015.

Base year selection can influence the apparent level of an index and its interpretability, especially when comparing indices from different countries or time periods. Care is taken to note the base year and any rebasing when presenting results; chain-linking and fixed-base methods affect how changes are tracked over time.