Plotting question

IMHO:

On 11-08-01 5:44 AM, Andrew McCulloch wrote:

Hi,

I use R to draw my graphs. I have 100 points on a simple xy-plot. The
points are
distinguished by a third variable which is categorical with 10 levels. I
have
been plotting x against y and using gray scales to distinguish the level
of the
categorical variable for each point. It looks ok to me but a journal
reviewer
says this is not any use. I cannot afford to pay for colour prints. Any
ideas on
what is the best way to distinguish 10 groups on an xy scatter plot?

Plot digits or letters or other symbols.

Duncan Murdoch

No, this does not work. See Cleveland's books (e.g. "Visualizing
Data"). 10 is too many symbols to constantly refer to a legend to keep
straight, and digits or letters do not allow you to readily perceive
the pattern. (Caveat: If "most" of the data are only 2 or 3 of the
symbols, then these can work).

I think the OP's idea of using gray scales was better. I would dispute
the reviewer and refer them to appropriate references. Alternatively,
thermometer plots (aka "filled rectangle" plots) would be best. Again,
Cleveland's books provide scientific justification rather than merely
the (possibly uninformed) aesthetic opinion of a reviewer. Presumably,
the journal editor would accept hard data and psychological research
in preference to opinions.

If all else fails I can just remove the graph and give them a table of
regression coefficients.

No. I think your attempt to use a graph is a much better way to go.
Try to resist poor practices such as just publishing summary
statistics.

Cheers,
Bert

Thanks.

Yours Sincerely
Andrew McCulloch

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______________________________________________
R-help at r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.

"Men by nature long to get on to the ultimate truths, and will often
be impatient with elementary studies or fight shy of them. If it were
possible to reach the ultimate truths without the elementary studies
usually prefixed to them, these would not be preparatory studies but
superfluous diversions."

-- Maimonides (1135-1204)

Bert Gunter
Genentech Nonclinical Biostatistics