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RE: st: Graph bar with label wtih % symbol at the top of each bar


From   Nick Cox <n.j.cox@durham.ac.uk>
To   "'statalist@hsphsun2.harvard.edu'" <statalist@hsphsun2.harvard.edu>
Subject   RE: st: Graph bar with label wtih % symbol at the top of each bar
Date   Fri, 11 May 2012 11:49:54 +0100

On this point you can find authorities to support any prejudice.

If I dissect this attitude, I find these thoughts -- in others; I will let David spell out his own arguments if they differ --

1. Giving numbers too is redundant, as it's the job of bar height or length to denote magnitude.

2. Giving numbers too makes a graph too busy, i.e. too detailed or complicated, to be really effective.

3. Figures are figures, and tables are tables, and ne'er the twain shall meet.

On #1, I see the point, but numbers too give the information in a different form and that can be helpful or even useful as well. "60% of Stata users do that! I didn't know the figure was so high" or whatever. The number can be read off the graph at least approximately, to be sure, but sometimes the exact value is the take-home message that means most to the audience, and giving it to them is a nice thing to do. In teaching I use a bar chart with continent areas; even geographers need to be told, or reminded, quite how big Antarctica is, for example, and giving them a number too is reasonable.

On #2, I think the answer is try it and see. A bar chart with three bars, the example that started this thread, could seem bare or even trivial without some annotation, but if the numbers are important, they are likely to enhance the graph. A bar chart with thirty bars could well look too crowded with the numbers too, and it is less likely that they will be legible. 

On #1 and #2, I do think there is a good case if you show numeric values, you don't need a numeric axis with numeric labels too. 

On #3, I think that is a convention to be ignored or flouted whenever it gets in the way of understanding the data. David and I share John Tukey as a statistical hero, and Tukey urged the mixing of graph and table ideas whenever it helped. Stem-and-leaf plots are perhaps the most obvious example, although not necessarily the best. 

I was looking again recently at 

Willard C[ope] Brinton. 1914. Graphic methods for presenting facts. New York: Engineering Magazine Company.

Brinton was the Edward Tufte of his day, even to the extent of self-publishing his magnum opus

Brinton, W.C. 1939.  Graphic presentation.  New York: Brinton Associates.  http://www.archive.org/stream/graphicpresentat00brinrich

Much of what he said in 1914 bears repetition. His advice on this point seems quite well balanced: 

"Whenever possible, include in the chart the numerical data from which the chart was made." (p.361)

"If numerical data cannot be included in the chart, it is well to show the numerical data in tabular form accompanying the chart." (p.362)

P.S. a few more highlights from Brinton (1914): 

"The circle with sectors is not a desirable form of presentation" (p.6)
-- as not so flexible as divided horizontal bar

[the term "pie chart" was introduced later] 

"the horizontal arrangement lends itself more readily to the use of type so that the reader may read type statements without having to turn the book" (p.7) (cf. p.41)

"Graphic comparisons, wherever possible, should be made in one dimension only." (p.22) (e.g. the use of bars of different lengths)

"Avoid using areas or volumes when representing quantities.
Presentations read from one dimension only are the least likely to be misinterpreted." (p.361)

"The general arrangement of a chart should proceed from left to right."
(p.361)

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

On Fri, May 11, 2012 at 1:46 AM, David Hoaglin <dchoaglin@gmail.com> wrote:
> Good practice for bar graphs does not put numbers on top of them.  If 
> you need to show the numbers, they should be in a table.

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