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Re: st: Dear All--I am trying to graph Conditional Quantile Function as a bar chart? Is there any way I can add the St.Err as a cap in bar chart for stata? Thanks--Hossein


From   David Hoaglin <dchoaglin@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Dear All--I am trying to graph Conditional Quantile Function as a bar chart? Is there any way I can add the St.Err as a cap in bar chart for stata? Thanks--Hossein
Date   Mon, 20 May 2013 07:55:32 -0400

Dear Hossein,

Your question is closely related to a thread that started on May 8.
I'll quote my initial advice in that discussion and then quote
comments from Nick Cox.  The link ending in "Poster3.pdf" is a good
1-page discussion of reasons for not making such plots.

David Hoaglin

My initial advice:

A good first step would be to omit the bars entirely.  Freeman et al.
(2008) discuss that type of plot under the name "dynamite plunger
plot" in their chapter "How to display data badly."  The bars take up
space to no good purpose.  A more effective plot would show the
estimates with error bars or confidence intervals (and an explanation
of whether the intervals are error bars or confidence intervals).

David Hoaglin

Freeman JV, Walters SJ, Campbell MJ (2008). How to Display Data.  BMJ Books.

The comments from Nick Cox:

I agree strongly with David.

I think I heard the term "detonator plots" from Stata user and
Statalist member Paul Seed at a users' meeting several years ago. He
may care to comment on whether it's his coinage.

Independently of that, and echoing David, it's my impression that the
term "dynamite plot" is more common.

Naturally what you call the beast is not central here, but it is
germane in so far as searching for "dynamite plot" on the internet
yields good discussions such as

http://biostat.mc.vanderbilt.edu/twiki/pub/Main/TatsukiRcode/Poster3.pdf

The key issues are (to me)

1. Such plots omit detail which you should care about showing (when
it's your data) or examining (always).

2. The visual signal strongly emphasises mean values relative to zero,
by the solid or thick bars, and plays down uncertainty, shown by the
intervals. Comparison with zero can be an important comparison, but
it's often not of scientific interest or concern.

A much more informative display is available through (e.g.)
-stripplot- (SSC) which allows error bars to be shown with raw data.

In terms of what Ronnie wants to do in Stata, his question is
puzzling, because the UCLA FAQ he cites explains in detail that -graph
bar- is a dead end here and you must switch to -twoway bar-.

Nick
njcoxstata@gmail.com
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