Date: Thu, 26 Apr 2007 11:58:57 -0400
Reply-To: Mark A Davenport MADAVENP <M_Davenport@uncg.edu>
Sender: "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From: Mark A Davenport MADAVENP <M_Davenport@uncg.edu>
Subject: Re: Question: Use (misuse, non-use) of error bars
In-Reply-To: <cad0d1200704260856w5700838bqf22d2f2c5e6ef273@mail.gmail.com>
Content-Type: text/plain; charset="US-ASCII"
This PowerPoint presentation by Jody Culham was also very helpful
http://defiant.ssc.uwo.ca/Jody_web/Culham_Lab_Docs/Advice/ErrorBars_Lecture5.ppt
***************************************************************************************************************************************************************
Mark A. Davenport Ph.D.
Senior Research Analyst
Office of Institutional Research
The University of North Carolina at Greensboro
336.256.0395
M_Davenport@uncg.edu
'An approximate answer to the right question is worth a good deal more
than an exact answer to an approximate question.' --a paraphrase of J. W.
Tukey (1962)
"Alexander J. Shackman" <shackman@wisc.edu>
Sent by: ajshackman@gmail.com
04/26/2007 11:56 AM
Please respond to
ajshackman@gmail.com
To
"Mark A Davenport MADAVENP" <M_Davenport@uncg.edu>
cc
SPSSX-L@listserv.uga.edu
Subject
Re: [SPSSX-L] Question: Use (misuse, non-use) of error bars
http://psyphz.psych.wisc.edu/%7Eshackman/mediation_moderation_resources.htm#Resources_for_Within-Subjects_%28Repeated_
the unpublished paper by christian schunn is particularly insightful
hth, alex shackman
On 4/26/07, Mark A Davenport MADAVENP < M_Davenport@uncg.edu> wrote:
Dear colleagues,
I have been working on a project wherein I am creating charts to show how
mean GPAs compare ACROSS several different ability goups and BETWEEN two
residential groups. I have done the sig tests and all, but am developing
charts to SHOW the data some administrators. Yes, I can show tables of
numbers and p values, and present statments that mean 1 is significantly
greater than mean 2, etc. Honestly, that is not really what this audience
is interested in. I really don't think tables of numbers will make an
impact.
The charting scheme I use makes use of error bars to show the uncertantly
of my point estimates. As I began thinking about the numbers I had
available (SDs, SE, 95% CIs, I began to wonder, 'Which should I use?" I
have used CI and never reall considered an alternative (perhaps due to the
nature of my research). I figured someone out there had a really good
answer. Well, I have been disappointed. My research has revealed the
following:
Whether you use SE, SD of CI depends largely on your discipline, your
question, your sample size..., etc. Strangely enough, I really don't
recall a common use of error bars in the education/psych journals that I
grew up with. All this is a slam in the face of my hero (cited below) and
inventor fo the box plot, John Wilder Tukey, who would have considered the
display of uncertainly in charts nothing less than standard (read,
required) practice. SPSS certainly makes it easy enough to include each
of the 3 types and alter the criteria (CI 90%, SE*2, etc.).
OK, all of that to ask this: Have you all, in your years of experience and
practice developed an opinion about the proper (or preferred) use of SD,
SE, CI error bars in particular suituations or with particular audiences
in the social sciences? Do you prefer SE (typically about half the width
of CI with decent sample sizes)? Do you even think it's important? I
really wonder at this last question, considering the lack of use in the
published ed and psych literature.
I respectfully surrender the soapbox to the next confused (or bored) soul.
Mark
***************************************************************************************************************************************************************
Mark A. Davenport Ph.D.
Senior Research Analyst
Office of Institutional Research
The University of North Carolina at Greensboro
336.256.0395
M_Davenport@uncg.edu
'An approximate answer to the right question is worth a good deal more
than an exact answer to an approximate question.' --a paraphrase of J. W.
Tukey (1962)
--
Alexander J. Shackman
Laboratory for Affective Neuroscience
Waisman Laboratory for Brain Imaging & Behavior
University of Wisconsin-Madison
1202 West Johnson Street
Madison, Wisconsin 53706
Telephone: +1 (608) 358-5025
FAX: +1 (608) 265-2875
EMAIL: shackman@wisc.edu
http://psyphz.psych.wisc.edu/~shackman
