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Re: st: plotting a regression function with time-dummies indicating structural breaks


From   Nick Cox <njcoxstata@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: plotting a regression function with time-dummies indicating structural breaks
Date   Tue, 3 May 2011 10:29:37 +0100

This is presumably a family of four curves given by a range on TIME_t
and Dummy_1 = 0, 1 and Dummy_2 = 0,1.

-twoway function- will take care of TIME_t = x but it is completely
dumb about the dummies. My guess is that it will use Dummy_1[1] and
Dummy_2[1] and give you just one of the four depending on values in
the first observation.

You will need to call -function- four times, but you don't need to
type the code four times.

Something like this:

forval a = 0/1 {
    forval b = 0/1 {
          local fcall `fcall' (function y = b_0 + b_1*x + `a'*(b_2 +
b_3*x) + b_4*`b', ///
          range(TIME_t))
    }
}

twoway (tsline y) `fcall' , legend(order(2 "0 0" 3 "0 1" 4 "1 0" 5 "1 1"))

I am assuming that this is generic code or that you have scalars b_0 .. b_4.

By the way, the -generate- line is irrelevant. -twoway function- works
with a generic x.

On Tue, May 3, 2011 at 10:10 AM, Oliver Jones
<ojones@wiwi.uni-bielefeld.de> wrote:

> I wonder if there is an easy way to plot a regression of the form:
>
> y_t = b_0 + b_1*TIME_t + Dummy_1*(b_2 + b_3*TIME_t) + b_4*Dummy_2
>
> So far I tried:
> gen x = TIME_t
> twoway ///
>        (tsline y) ///
>        (function y = b_0 + b_1*x + Dummy_1*(b_2 + b_3*x) + b_4*Dummy_2, ///
>                range(`first_year' `last_year'))
>
> I seem to have a problem with the range, because the resulting graph just
> covers one third of the graph. But the shape seems to look ok, just
> compressed.
>
> Hopefully there is a nice way of plotting such stuff without the -function-
> command or some one has a hint regarding the range problem.

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