Why aggregation changes forecast error

Forecasting is a structured estimate for a defined decision, horizon and level of detail. This guide introduces why aggregation changes forecast error and shows where it fits in a practical planning cycle.

Practitioner lens

Keep the decision in view when using why aggregation changes forecast error. A forecast for replenishment, capacity and annual budgeting may need different horizons and different levels of aggregation.

First experiment

Draw the series before fitting a model; mark missing periods, stockouts, promotions and calendar changes.

This is an original educational brief. It is a starting point for discussion, not a claim that one technique fits every supply chain.