Time Series for Business: Stationarity, ARIMA, Forecasting

Junior quantitative analysts at Helio Verde Beverages build a robust 12-month SARIMA-with-break-dummy forecasting framework on real monthly Cola sales (2018-2025, 96 obs), confront the April-2024 structural break, compare against Holt-Winters, VAR, Prophet and LSTM, and learn the M-competition empirical regularity that simple combination methods quietly win. Eight Box-Jenkins decision rounds drive MAPE from the 18% Excel baseline toward the 11% combination floor, with 80%/95% prediction intervals and explicit calibration audit.