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

[Oliver Jones <ojones@wiwi.uni-bielefeld.de>]

Hi Nick,
here is some example I just made up, that shows what I mean by "range problem"

************* begin example ****************
clear
set obs 20

gen int TIME = _n + 1990

* create dummies
gen byte d1 = 0
replace d1 = 1 if TIME > 1995
gen byte d2 = 0
replace d2 = 1 if TIME > 2005

tsset TIME

* set coefficients
scalar b_0 = 100
scalar b_1 = 2
scalar b_2 = 10000
scalar b_3 = -5
scalar b_4 = 20

* generate the time series
set seed 1
gen u = rnormal(0,2)
gen y = b_0 + b_1*TIME + b_2*d1 + b_3*d1*TIME + b_4*d2 + u

tw ///
	(tsline y) ///
	(function y = b_0 + b_1*x + b_2*d1 + b_3*d1*x + b_4*d2, ///
		range(1991 2010)), ///
	legend(order(1 "tsline" 2 "function"))

************* end example ****************

I hope the resulting plot shows what I mean.

Best
Oliver


Am 03.05.2011 11:29, schrieb Nick Cox:
> 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.
>
> *
> *   For searches and help try:
> *   http://www.stata.com/help.cgi?search
> *   http://www.stata.com/support/statalist/faq
> *   http://www.ats.ucla.edu/stat/stata/

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