On Thu, 13 Jan 2011, [big5] ������ ������ wrote: You can calculate MAPE for any series over any range by setting the sample range and applying the simple formula: MAPE = sum(abs(y)) / $nobs We decided it was best to display these as z-statistics for estimators whose validity is based on asymptotic theory and where standard errors are based on ML estimation. That may be dabatable, but it's a legitimate choice. Allin Cottrell