Random variation
Unexpected events, measurement noise and other short-lived influences can produce fluctuations around estimated trend and seasonal patterns. A residual in a fitted model is an observed difference between actual and fitted values; its interpretation depends on the model and may include more than pure randomness.
Worked example
An unusual one-off power outage reduces one month’s sales below the seasonal forecast. The unexpected shortfall may be treated as an irregular component after investigating its cause.
Common mistake
Assuming every residual is random noise without checking whether a systematic pattern or data error remains.
Where it appears in your exams
| Qualification | Exam | Relationship | Period |
|---|---|---|---|
| ACCA | MA | Direct | September 2026–June 2027 |
| FIA | FMA | Direct | September 2026–June 2027 |