Mean Squared Error (MSE) And Root MSE (RMSE)

This is a very common measure for evaluating the accuracy of the forecast.  The square root of this measure is also used (RMSE).  Both MSE and RMSE tend to be overly affected by outliers.  However, it is implicitly assumed that the MSE measure is zero.  Stated differently, when the MSE is zero, then the forecasting model is unbiased.