Excel Moving Average and Seasonal Forecast Lesson With Honest Limits
Learn simple forecasting and when not to trust it.
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Teach me simple forecasting in Excel using my data. A monthly series with at least 24 values (invented or anonymised): [MONTHLY_SERIES]. The decision the forecast supports: [DECISION]. Explain moving averages, seasonal indices (the average of each month divided by the overall average) and a simple trend line. Arithmetic example: if each January in two years of monthly sales is 20 percent above average, its seasonal index is 1.2. Walk through building the forecast in a worksheet, comparing it with actuals for the last six months (error as actual minus forecast, and absolute percentage error), and giving a range of plausible values instead of one number. Mention built-in forecasting functions and their assumptions [VERIFY]. State plainly that a forecast is an estimate from the past, unusual events break it, and I should record the assumptions. Always compare with actuals and show the error. Return a step list and the checks. Function availability and menu names differ by version; mark anything you cannot confirm [VERIFY] and tell me how to check.
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