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Re: st: overlapping histograms


From   Jeph Herrin <junk@spandrel.net>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: overlapping histograms
Date   Mon, 29 Sep 2008 16:46:29 -0400

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.






Nick Cox wrote:
Do you mean something like this?

sysuse auto

twoway histogram mpg if foreign, start(10) width(2) bfcolor(none) blcolor(red)
|| histogram mpg if !foreign, start(10) width(2) bfcolor(none) blcolor(navy) barw(1.9) legend(off)




Jeph Herrin wrote:

Yes, a colleague specifically wants histograms, and he knows
his audience, presumably. More pointedly, he also has a
figure just like he wants, from an unknown source, which is
clearly created in Stata. However, the solution there is to
narrow the bars in the top histogram, while leaving those in
the back full width. This works well visually - the eye is
tricked into seeing both distributions at once, despite a great
deal of overlap, except I'm not happy that the bars are not
the same width. So I'm trying to improve on it, while sticking
close to what it is.

Thanks to others for their suggestions.

cheers,
Jeph





Nick Cox wrote:
Jeph may be acting under orders, i.e. someone is insisting on something like this, but the problem that one obscures the other presumably arises because your distributions are not too different and is likely to persist with any small modifications to the recipe.

In addition to other solutions suggested, -qqplot-, -qplot- (SJ), -distplot- (SJ), -stripplot- (SSC), -beamplot- (SSC) are some commands I would use to compare distributions graphically long before I tried to superimpose histograms.

Nick
n.j.cox@durham.ac.uk

Jeph Herrin wrote:

I've been trying to create a graph which shows
two overlapping histograms - I'm trying to show
how the distribution for a quantity if interest
has shifted from time A to time B.

Putting two histograms on one graph is not the
problem

 twoway (histogram myvarA) (histogram myvarB)


but the problem is that one obscures the other. I
can make the one on top "clear" (specify -color(none)-)
but because the bars line up it still difficult to
distinguish them. So I'm looking for a way to do
either

1. make the overlapping areas a darker color than
   either histogram is alone
2. shift the bars for one histogram so that the one
   behind can be seen ever so slightly

Is there a way to do either? Is there a better solution?
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