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Re: st: detonator plot with three grouping variables


From   "Roger B. Newson" <r.newson@imperial.ac.uk>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: detonator plot with three grouping variables
Date   Thu, 09 May 2013 12:05:27 +0100

My take on detonator plots is that they CAN be useful, and complementary to the CI plots for differences, because an audience presented with mean or prevalence differences will frequently ask what these differences are differences between. The important thing (I find) is to make both confidence limits visible, which of course makes the bars look a little bit less like detonators. People commonly make the mistake of coloring the bars black, and leaving the comfidence limits black too, which makes the bars look a bit more like detonators. I usually color the bars white, or light shades of grey.

The -eclplot- package, downloadable from SSC, is my usual tool for making detonator plots, specified by the options

eplottype(bar) rplottype(spike)

or

eplottype(bar) rplottype(cap)

depending on whether or not I want the confidence limits to have caps. And I usually use my graphics scheme -scheme_rbn1mono-, which you can also download from SSC, and which usually colors bars white, or fairly light shades of gray, unless instructed to do otherwise. And -eclplot- will usually put the confidence limits in the foreground, and the bars in the background, unless instructed otherwise.

I hope this helps.

Best wishes

Roger


Roger B Newson BSc MSc DPhil
Lecturer in Medical Statistics
Respiratory Epidemiology and Public Health Group
National Heart and Lung Institute
Imperial College London
Royal Brompton Campus
Room 33, Emmanuel Kaye Building
1B Manresa Road
London SW3 6LR
UNITED KINGDOM
Tel: +44 (0)20 7352 8121 ext 3381
Fax: +44 (0)20 7351 8322
Email: r.newson@imperial.ac.uk
Web page: http://www.imperial.ac.uk/nhli/r.newson/
Departmental Web page:
http://www1.imperial.ac.uk/medicine/about/divisions/nhli/respiration/popgenetics/reph/

Opinions expressed are those of the author, not of the institution.

On 09/05/2013 11:49, Nick Cox wrote:
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

On 9 May 2013 04:47, David Hoaglin <dchoaglin@gmail.com> wrote:
Ronnie,

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.

On Wed, May 8, 2013 at 5:49 PM, Ronnie Babigumira <rb.glists@gmail.com> wrote:

I am trying to create a detonator plot like the one in this example http://www.ats.ucla.edu/stat/stata/faq/barcap.htm only I have 3 levels. Here is an example using the accessible auto data

sysuse auto,clear
egen lwst = fill(1,2,1,2)
recode rep78 (1 2 = 3)

What I would like to do is add error bars to this plot

gr bar price, over(lwst) over(foreign) over(rep78)

Any help is much appreciated

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