Re: st: overlapping histograms

[Nick Cox <n.j.cox@stata.com>]

Or, more naturally,

gen gpm1 = 1/mpg1
gen gpm0 = 1/mpg0
qqplot gpm0 gpm1

i.e. the reciprocals of mpg differ by an additive shift.


Nick Cox wrote:
> It is good to know that you can do this. My guess is that many users 
> would like to see it written up somewhere.
>
> However, these histograms tend to lead only to crude inferences. Users 
> can't read off quantitative conclusions from the graph, just stuff like 
> "The distributions are about the same", or "... very different", etc.
>
> Compare the road that begins
>
> . separate mpg, by(foreign) veryshortlabel
>
> . qqplot mpg1 mpg0
>
> . qqplot mpg1 mpg0, xsc(log) ysc(log)
>
> That is the start of a story: the distributions differ multiplicatively,
> etc. Numbers can be then worked out.
>
> Nick
>
> Svend Juul wrote:
>
> > Jeph wrote - in a comment to several suggestions:
> >
> > More like this:
> >
> > sysuse auto
> >
> > twoway ///
> > (histogram mpg if foreign, bin(10) gap(5) fc(gray) lc(black)) ///
> > (histogram mpg if !foreign, bin(10) gap(15) fc(white) lc(black)) ///
> >    legend(off)
> >
> > It works better when there are more bins, ie, more obs - I have 100k
> > obs so I have lots of thin bars. The effect is quite good, though
> > I dislike that, as here, one distribution has thinner bars than the
> > other.
> >
> > ================================================================
> >
> > Fascinating game. How about this?
> >
> > twoway ///
> > (histogram mpg if !foreign, start(10) width(2) fc(white) lc(black)) ///
> > (histogram mpg if foreign, gap(50) fc(gray) lc(black) start(10)
> > width(2)) ///
> >    , legend(off) plotregion(margin(b=0))
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