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st: AW: RE: how to control jitering in scatter plots


From   "Jann, Ben" <ben.jann@soz.gess.ethz.ch>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: AW: RE: how to control jitering in scatter plots
Date   Wed, 6 Aug 2003 11:07:09 +0200

Thanks for your reply, Nick. 

Maybe I didn't express myself clear enough. What I expected was that

 . set seed 3562
 . scatter y x, jitter(2)
 . set seed 3562
 . scatter y x, jitter(2)

would produce two identical graphs, just as

 . set seed 3562
 . gen v1=uniform()
 . set seed 3562
 . gen v2=uniform()

produces two identical variables. This, however, is not the case. Ergo, the jitering does not seem to depend on the seed (unless I miss something here).

Of course, Nick's solution (creating random perturbations outside -scatter-) would work. I just thought it would be nice to have full control over the jitering-option without having to use a backdoor. And, by the way, I am really curious how the jitering is determined if not by the seed. (because I feel commited to the scientific reproducability policy ... although this might be splitting hairs in this case)

ben


> -----Ursprüngliche Nachricht-----
> Von: Nick Cox [mailto:n.j.cox@durham.ac.uk] 
> Gesendet: Dienstag, 5. August 2003 17:59
> An: statalist@hsphsun2.harvard.edu
> Betreff: st: RE: how to control jitering in scatter plots
> 
> 
> Ben Jann
> > 
> > Does anyone know how the random noise generator of the 
> > jitering option in scatter plots can be controlled (Stata 8 
> > and/or 7). I'd like to produce a series of related graphs 
> > for didactical purposes. The data points are always the 
> > same, however, some other stuff changes from graph to 
> > graph. It would be really nice if the data points would be 
> > jittered *exactly* the same way in each graph. (Up to now, 
> > I just produced one graph with everything in it, and then 
> > manually deleted whatever wasn't needed by editing the eps-file.)
> > 
> > My first guess was, that the jittering depends on the seed. 
> > So I tried:
> > 
> >  set seed ...
> >  scatter ...
> > 
> > This doesn't work, however.
> 
> I guess that the jittering does depend on 
> the seed, but it won't remain constant 
> from graph to graph, any more than you 
> get the same sample of random numbers 
> repeatedly even if the seed remains unchanged. 
> 
> For your purposes, I think you will need to produce  
> one or more sets of random perturbations outside 
> -scatter- and then add to your variables. To 
> ensure that the perturbed variables have the 
> same variable labels, value labels, format, 
> etc. as your originals, there are various commands, among which 
> -copydesc- on SSC is in the public domain. 
> 
> Nick 
> n.j.cox@durham.ac.uk 
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