Symmetric mean absolute percentage error

Symmetric mean absolute percentage error (SMAPE) is a measure of how accurate a model's predictions are. It is calculated by subtracting the prediction from the actual observed value, taking the absolute value of the result, and then dividing by the actual value. This gives you the "error" (how much off the prediction was). You then take the average of all of these errors for the model. The lower the SMAPE value, the better the model's predictions are.