Calculating percentage prediction error: a user's note.

The equations of calculation of percentage prediction error (percentage prediction error = [equation: see text] x 100 or percentage prediction error = [equation: see text] x 100) and similar equations have been widely used. However, not much is known about the property of this type of equation and the caution which should be taken into account when using this type of equation. Moreover, little is known about the power of percentage prediction error as statistical inference. In the present study we address these points in the use of this type of equation.