Dear all: I have two questions: 1. If I use data from 1980M01 to 2000M12 to estimate the model(in-sample forecasting). It can calculate the MAPE of 1980M01-2000M12. Can it just calculate the MAPE of within-sample like 1999M1-2000M12、1998M01-2000M12 or so on in gretl? 2. Why does the test of AR and MA show t-statistics in gretl1.8.4, but z-statistics in gretl1.9.1? Their values in my sample are the same. But degree of freedom of t distribution in my sample is not large, so the values of t-statistics (gretl 1.8.4) and z-statistics (gretl 1.0.1) should not be the same. It seems that they are both z-statistics, but it shows t –statistics in gretl1.8.4. Doesn't it test with t-statistics in general? Why does gretl use z-statistics? Thanks a lot