uncertainty-chartslisted

# Uncertainty charts A single forecast line is a claim of certainty that no forecast supports. The reader takes the number off the chart, quotes it, and the range that mattered is gone. The purpose of every chart here is to keep the range visible. --- ## Fan chart — forecast with widening uncertainty Actuals as a solid line; from the forecast boundary, nested bands of increasing width. ``` ╱▒▒▒▒▒ ╱▒▒▒▓▓▓▓▓▓ ────────────────●═══════════╱▒▓▓███████████████ ╲▒▒▒▓▓▓▓▓▓▓▓ ╲▒▒▒▒▒▒ actuals forecast → ``` - **Bands widen with horizon.** A constant-width band implies uncertainty does not grow with time, which is false for every business forecast. - **Two or three bands, not five.** Typically a central case plus one or two ranges. More bands read as precision about imprecision. - **Label what the bands mean** — and be honest. If they are scenario judgements rather than statistical intervals, call them "scenario range", not "80% confidence". Dressing judgement in statistical language is the most common dishonesty in forecast charts. - **Central line dashed** past the boundary; solid for actuals. - **Do not extend bands beyond where you have a view.** A 5-year fan from a 12-month model is decoration. --- ## Scenario bands — discrete cases When you have named scenarios rather than a distribution: - **Three lines: base, upside, downside.**