The history you forecast from
Every forecast is a claim about a series. What is wrong with the series is usually what is wrong with the forecast.
Every Forecast Is a Claim About a Series
A forecast is a statement about a historical series. What is wrong with the series is usually what is wrong with the forecast, and it is examined last.
How Much History Is Enough
How many periods a forecast needs to see a season, a trend or a driver effect, and what to do when the series is shorter than the question requires.
The Definition Changed and Nobody Said
How a reporting change becomes a fake trend, the six places definitions change, and the one-line record that prevents years of misreading.
Gaps, and What Filling Them Does
Three kinds of gap in a demand series, why the fill method matters more than the gap, and how a filled value becomes a measurement nobody questions.
The Outlier That Was a Real Day
When to remove an extreme value from a demand series and when removing it destroys the thing you needed to know, with the three questions that decide.
Breaks: When the Past Stopped Applying
How to recognise that a series has changed regime rather than moved, what to do with the history before the break, and why waiting is usually right.
Cleaning a Series Without Inventing One
The order in which to clean a demand series, what to leave alone, and the rule that separates legitimate cleaning from quietly fabricating history.