'IF' statement for time periods in models

[jaime.nie]

Good morning,

I am using Eviews 12 and programming a model that spans from 1971 to 2018 (yearly). My problem is the following:

While the vast majority of the explanatory variables have available data from 1971-2018, some dependent variables depend on explanatory variables only available from 1998 onward. So, the non-problematic equations with explanatory variables spanning 71-18 would be like this:

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Y1= B0+B1X1+B2X2+B3X3 +...

And the few (but important) problematic equations look like this:

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Y1=(B0*+B1*X1*+B2*X2*+B3*X3*+...)

with X3 spanning from 1998-2018.

We previously tried to solve the issue by the following method, suggested in this forum:

First, we estimated two different equations, one from 71-97 and another 98-18. Then we write this in the model window:

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Y1= (@year<1998) *(B0+B1X1+B2X2+B3X3+...) + (@year>=1998)* (B0*+B1*X1*+B2*X2*+B3*X3*+...)

It worked as long as the dependent variable for both equations had the same form, say: Y1 for both equations are in logs, or in first difference, or levels... Otherwise, it became problematic, i.e. the model crashes. So, as a simple solution, valid for running the model for out-of-sample forecasting purposes, we kept the 98-18 equation and excluded in scenarios that variable from 71-97. However, this is not good enough for counterfactual analysis.

Therefore, I was looking into 'if then else' statements in Eviews, but I am not being able to make it work. So, this is what I am writing:

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if @year>=1998 then Y1=B0*+B1*X1* + B2*X2* + B3*X3* +... else Y1=B0+B1X1 + B2X2 + B3X3 +... endif

It does not work either when I write the equations as :eq1 and :eq2 instead of the "substituted coefficients" form.

I hope this all makes sense. Could I get help to solve this issue? Many thanks in advance.

Kind regards

[EViews Gareth]

@recode