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ARMA equation

Posted: Tue Aug 28, 2018 6:36 am
by guido
I struggle to understand the difference between this two models, when generating an equation in EViews:

gdp gdp(-1) gdp(-2)
gdp ar(1) ar(2)

Are not those the same? Unfortunately EViews returns different values, especially when I add a constant and a trend.

Re: ARMA equation

Posted: Tue Aug 28, 2018 7:08 am
by startz
AR terms refer to lags of the error term. In an equation with no error term, that's the same as lags of the dependent variable. Otherwise not.

The other difference is that by default EViews uses slightly different estimation techniques for AR than for lags. Generally, it makes very little difference.