[R] Diamond graphs

[David Scott]

On Thu, 21 Aug 2003, Baize, Harold wrote:

> Richard A. O'Keefe  <ok at cs.otago.ac.nz> wrote:
> 
> > Someone mentioned the new "Diamond Graphs" invented at Johns Hopkins.
> > I haven't see the August 2003 issue of The American Statistician yet,
> > but I _have_ read the press release.
>   
> Same here.
>  	
> > The fact that someone would try to patent this strikes me as outrageous;
> > the actual amount of novelty is so tiny.
>  

Miss out a lot of stuff here

> Less expensive and more practical would be to present the data in 
> a two dimensional matrix (as proposed in the "diamond") but not 
> to use an odd shape to convey the third dimension. The third 
> dimension could be represented by hue (color) or brightness (shade). 
> I suspect that actual psychometric tests would show that color 
> or other visual representations of density would be more accurate 
> and reliable than their proposed solution which confounds area with 
> shape. 
> 
> As a caveat, I have not read the American Statistician article. 
> I will be surprised if they present data showing that users 
> can more accurately perceive variation in the continuous variable 
> through their odd shape solution in contrast to either color or 
> shade.
> 

Since no-one so far has replied with a reference to Cleveland, I guess I
will. Cleveland in "Elements of Graphing Data"  reports on his experiments
in graphical perception. He has examined the accuracy of decoding
information which has been graphically encoded using various approaches.
Colour hue, colour saturation and density (amount of black) are the
poorest of all the approaches he considers, and rank below area and
volume.

The bias involved in using area and volume to represent numerical 
quantities is an additional complication which I believe Richard O'Keefe 
also mentioned.

For those who are not aware of Cleveland's work, it would be fair to say 
that you see his influence (and that of others from Bell Labs) every time 
you ask R to produce a graph.

David Scott
_________________________________________________________________
David Scott	Department of Statistics, Tamaki Campus
		The University of Auckland, PB 92019
		Auckland	NEW ZEALAND
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Email:	d.scott at auckland.ac.nz 


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