On 24 Samh 2009, at 15:29, Ariel Linden, DrPH wrote:
That said, there are some audiences that prefer to see something
that looks
and feels like a histrogram or density curve to see how the
distributions
overlap (or don't). In this situation, I usually offer up a couple
different
methods of visually describing the data.
I know people like something that looks like histograms, but
histograms fail one of the fundamental rules of graphics: you
shouldn't be able to make two different graphs of the same data.
sysuse auto, clear
histogram mpg, name(Default, replace) title(Default)
histogram mpg, width(5) start(10) name(Bin5Start10, replace)
title("Bin 5 Start 10")
histogram mpg, width(3) start(10) name(Bin3Start10, replace)
title("Bin 3 Start 10")
histogram mpg, width(3) start(12) name(Bin3Start12, replace)
title("Bin 3 Start 12")
graph combine Default Bin5Start10 Bin3Start10 Bin3Start12
The resulting display shows four histograms of the same variable, all
of which look different (and I didn't go to any trouble making up the
example - a little fiddling around would produce even more striking
differences).
Now: when four histograms of the same data differ by so much, how can
anyone tell which of the differences between any two histograms are
the result of arbitrary choices of start values and bin widths?
Ronan Conroy
=================================
[email protected]
Royal College of Surgeons in Ireland
Epidemiology Department,
Beaux Lane House, Dublin 2, Ireland
+353 (0)1 402 2431
+353 (0)87 799 97 95
+353 (0)1 402 2764 (Fax - remember them?)
http://rcsi.academia.edu/RonanConroy
P Before printing, think about the environment
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