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Hi, I want to do the out of sample forecasting. And I am a beginner to do programming.
My sample data ranges from 1929m07 to 2009m12. The equation is Yt=a+bXt-1. I want to use 20 years monthly return(1929m07 to 1948m 07) to forecasting the return of 1948m08 and then use 1929m08 to 1948m08 data to forecasting the return of 1948m09........on and on ....
Who knows how to do this programming...or you can teach me how to do the out of sample test.

Thank you so much.

You're actually describing a rolling forecast. For a beginner that can be a bit intimidating. There are lots of examples on the forum though. Reading through here is probably a good place to start:
http://forums.eviews.com/viewtopic.php?f=15&t=878

Thank you so much.