basismonthly

Basismonthly is a term used in time-series analysis to denote the standard baseline reference value for monthly data. It can refer to either a base month’s value used to construct an index, or to a baseline period whose average serves as the reference level for normalization.

One common implementation treats basismonthly as an index: I_t = (V_t / V_base) × 100, where V_t is the observed value in month t and V_base is the value in the chosen base month. By convention, the base month is set so that I_base = 100, making deviations easy to interpret.

An alternative uses a baseline period: B = average(V_t) over the months in the baseline window. Values in other months are then expressed relative to B, often by ratio or percent change.

Purpose: Basismonthly allows comparisons across months and datasets that differ in scale, facilitates growth and trend analysis, and supports adjustments for seasonality or inflation when used with an appropriate baseline.

Applications include finance and economics (indexing price series), marketing analytics (monthly performance benchmarks), health and climate research (normalized indicators), and any field using time-series normalization.

Calculation considerations: The choice of base month or baseline window impacts interpretation and should be clearly documented. When data are volatile, smoothing or selecting a longer baseline can stabilize basismonthly values.

Example: If the base month value is 200 and the observed value in month t is 210, the basismonthly index for that month is (210/200) × 100 = 105.

See also: baseline, index, normalization, time-series, seasonality.