Stage 2 · Intermediate · M7
Predicting Tomorrow
In a forecasting contest of 5,507 teams, most could not beat the rule that tomorrow looks like today.
15 lessons · 116 minSteady
About this chapter
A forecast is a guess about a number you have not seen yet, made from the numbers you have. This chapter builds forecasting from pictures you already know: Riyadh's year, a grid that follows the heat, a shop that fills up on Thursday and before Eid. You meet the simple forecasts that are hard to beat, learn to test a forecast the way time runs, give a range instead of one number, and decide when a forecast should not be made at all.
What you will be able to do
- 16 min
Yesterday Is a Clue
Read a time series as values in order, and say what the order carries that a shuffled list loses.
- 27 min
Three Things in One Line
Pull a series apart into trend, season and remainder, and say which of the three a forecast can use.
- 37 min
The Clocks Inside a Series
Find a season's length by counting from peak to peak, and spot a second clock hiding in the same series.
- 48 min
Tomorrow Looks Like Today
Make the last-value and last-season forecasts, and use them as the baseline any model has to beat.
- 57 min
Keeping Score
Score a forecast by its average miss at a stated horizon, and turn that miss into skill against a baseline.
- 68 min
Average the Recent Past
Forecast with a moving average, choose its window, and tell a line you could draw on the day from one that peeks ahead.
- 78 min
Let Old Days Fade
Forecast with exponential smoothing, read its weight as how fast old days fade, and pick that weight from the errors.
- 89 min
The Series Predicts Itself
Fit M1's straight line to a series' own past, choose which past steps it reads, and forecast several steps by feeding forecasts back in.
- 99 min
Two Calendars, One Shop
Turn the calendar into features, and line up a Hijri season with the Hijri calendar instead of the Gregorian date.
- 108 min
No Peeking
Split a series by time, and catch the three leaks that forecasting invites: shuffled splits, lags shorter than the horizon, and features built with the future.
- 119 min
Walk Forward
Test a forecast at several cuts that move forward in time, and compare two models on the average over those folds.
- 128 min
A Range, Not a Number
Draw a prediction interval, say why it widens with the horizon, and check its coverage on the future it claims to hold.
- 138 min
Big Models Against the Baseline
Say what forecasting contests found about simple and learned models, and name the settings where a big model earns its place.
- 148 min
Surprises
Flag an anomaly as a value far from its forecast, clean it before it echoes, and tell a real surprise from an expected holiday.
- 156 min
When Not to Forecast
Judge whether a series can be forecast with four questions, and say what to offer instead when it cannot.