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Excel MAPE
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Improvement
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Reference: Hyndman, R.J. & Athanasopoulos, G. (2021) Forecasting: Principles and Practice, 3rd ed., OTexts. Models: Excel Linear (OLS regression = FORECAST.LINEAR), Naive (random walk), Seasonal Naive (SNAIVE), SES (ETS(A,N,N)), Holt's Linear (ETS(A,A,N)), Holt-Winters Additive (ETS(A,A,A)). Smoothing parameters optimized via grid search. Prediction intervals: Holt-Winters via forecast error variance. Default scenario: 36 months (Jan 2023 – Dec 2025), trending+seasonal demand, base=2000, trend=15/mo, seasonal amplitude=400, noise SD=40, train/test split 24/12.