Define the forecast horizon and frequency
Daily, weekly, monthly, and annual forecasts behave differently. The chosen horizon should match the planning decision: staffing may require weeks, inventory may require months, and strategic budgeting may require years.
Build a baseline first
Simple baselines include the last observed value, the same period last year, a moving average, or a linear trend. Every advanced model should be compared with a baseline. Otherwise model complexity may create the illusion of improvement.
Use time-aware backtesting
Random train-test splits are usually inappropriate for forecasting because they allow future observations to influence the past. Evaluate the model by training on earlier periods and testing on later periods, ideally across several rolling windows.
Choose metrics carefully
MAE is easy to interpret in the target unit. RMSE penalizes large errors more strongly. MAPE expresses error as a percentage but behaves badly near zero and can distort comparisons. Metrics should reflect the practical cost of forecast errors.
Represent uncertainty
A single forecast line suggests false precision. Where the method supports it, show prediction intervals or scenario ranges. Explain what assumptions could make future values fall outside those ranges, including structural changes, promotions, market shocks, and missing external variables.
Connect forecasts to decisions
The useful output may be staffing ranges, inventory scenarios, budget thresholds, or alerts—not merely predicted numbers. The forecast should specify what action changes when the expected value or uncertainty changes.
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