MAPE and What-If - Forecast Error Metrics, Step by Step

MAPE uses actual values as the scale, and the what-if must be recomputed.

highlighted = computed this step

MAPE

MAPE averages absolute error divided by actual.

\text{MAPE}=\text{average}(|\text{error}|/\text{actual})

The exact MAPE is 7/48.

\text{MAPE}=7/48

The what-if changes the third forecast to 10.

\text{changed forecast}=10

The what-if gives MAD 1, MSE 1, and MAPE 13/144.

\text{what-if metrics recomputed exactly}