Mark,

I'm sure you will get more learned opinions than mine, but I have also struggled with the issue. I've never considered using CI, but wrestled with SE vs SD. As I understand it, the choice relates to your purpose: Use SE if you want to show how "close" your group means are likely to be to the population mean. Use SD if you are interested in showing the variability of your particular samples, without concern for the population values. Thus, if you are using statistical tests of significance, SE's are probably most appropriate. That's my 2 cents.

My piggy-back question: Is there a way in SPSS to have error bars appear on bar charts, particularly if using the GUI? I have yet to figure that one out.

Fred

-- Fredric E. Rose, Ph.D. Assistant Professor of Psychology Palomar College 760-744-1150 x2344 frose@palomar.edu

On 4/26/07 8:49 AM, "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)