baseperiode

Baseperiode is the reference time period used in index numbers and time-series analysis to measure relative changes. It serves as a starting point against which all other periods are compared. In most applications the base period is assigned a value of 100 (or 1), so that a period with a value higher than the base shows growth, while a value lower shows decline.

In practice, the baseperiode is chosen to be representative of the period of study, and the index for any period t is calculated as index_t = (value_t / value_base) × 100. The base can be fixed, meaning the same base period is used for all calculations, or chained, where the base is updated periodically to reflect more recent data and reduce distortion in long time spans. The choice between fixed-base and chain-base affects the interpretability of long-run trends and the ease of comparing distant periods.

Common uses of a baseperiode include consumer price indices, production or output indices, and other economic indicators. The base period provides a fixed reference point for assessing inflation, growth, or relative performance over time. Changing the baseperiode requires rebasing past values to maintain comparability, but the measured growth between periods can still be understood in consistent terms once the appropriate conversions are applied. Rebasing is often done to keep the base period recent and relevant for interpretation, or to improve numerical stability in long time-series analyses.