On the asymmetry of the symmetric MAPE

Several authors have suggested that the use of the mean absolute percentage error (MAPE) as a measure of forecast accuracy should be avoided because t hey argue it treats forecast errors above the actual observation differentl y from those below this value. To counter this, the use of a symmetric (or modified) MAPE has been proposed. This paper shows that, in its treatment o f negative and positive errors, the proposed modification is far from symme tric, particularly where these errors have large absolute values. It also s hows that, under some circumstances, a non-monotonic relationship can occur between the symmetric MAPE and the absolute forecast errors. (C) 1999 Else vier Science B.V. All rights reserved.