MAPE error forecast measurement

[mscarlatos]

My regression uses data from 1970Q1 to 2006Q4. I would like to assess the "forecastibility" of the results (ie., coefficients) for 2001Q1-2006Q4. Does MAPE generate coefficients through to 2000Q4 and then insert these resulting coefficients to forecast 2001Q1 onwards and then compare the forecast with the actual? Also, it seems the program default is for the entire period 70Q1-06Q4. Does this mean that the forecast of 70Q4, say, is based on coefficients generated before 70Q4? Any thoughts or direction would be appreciated.