Re: st: Use lag operators with interaction term, is it correct?

[Nick Cox <njcoxstata@gmail.com>]

This is a cross-posting of

http://stats.stackexchange.com/questions/67839/use-lag-operators-with-interaction-term-is-it-correct

The FAQ is quite explicit that you are asked to declare cross-postings.

Nick
njcoxstata@gmail.com


On 20 August 2013 09:57, Herman Haugland <herman.haugland@gmail.com> wrote:
> Hi, a newbie question here:
>
> I have a linear model that I am estimating using FE and RE,  in which
> my explanatory (continuous) variable is lagged, something like this:
>
>
> y = a + bx(t-1) + e
>
> Stata: xtregar y L.variable, fe/re
>
>
> For my analysis, I need to include a categorical interaction term.
> Stata, by using the graphical interface, does not allow me to use lags
> with my continuous variable, but it does give me results if I add 'L'
> manually, and these are very different to those without the L.
>
> What Stata graphical interface allows me to do is:
>
> xtregar y L.variable dummy#c.variable i.dummy, fe
>
>
> And what I need is:
>
> xtregar y L.variable dummy#Lc.variable i.dummy, fe
>
>
> I am confused since I imagine that if adding lags was OK, Stata would
> allow me to add them, wouldn't it?
>
> 1) Is it correct to add lags to an interaction term?
>
> 2) In case of that the answer to (1) is NO: If I remove the variable
> (L.variable), is it OK to add lags to the interaction term?
>
>
> I am using Stata 12.
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