11.1 Forecast, projection, scenario, or target?

A forecast learns from historical patterns. A projection calculates what would occur if stated assumptions hold. A scenario combines assumptions to examine a plausible future. A target is a desired outcome.

The forecasting framework in this chapter follows the general time-series principles developed by Hyndman and Athanasopoulos (Hyndman and Athanasopoulos 2021).

These terms should not be used interchangeably. A projected 10 percent increase under an assumed marketing effect is not evidence that the intervention will cause 10 percent growth. A target of 1,000 new members is not a forecast merely because it appears on a future timeline.

References

Hyndman, Rob J., and George Athanasopoulos. 2021. Forecasting: Principles and Practice. 3rd ed. OTexts. https://otexts.com/fpp3/.