Symmetric mean absolute percentage error (original) (raw)

Symmetric mean absolute percentage error (SMAPE or sMAPE) is an accuracy measure based on percentage (or relative) errors. It is usually defined as follows: where At is the actual value and Ft is the forecast value. The absolute difference between At and Ft is divided by half the sum of absolute values of the actual value At and the forecast value Ft. The value of this calculation is summed for every fitted point t and divided again by the number of fitted points n. Armstrong's original definition is as follows: