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Re: st: Plot means with SD


From   David Hoaglin <dchoaglin@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Plot means with SD
Date   Wed, 4 Apr 2012 11:35:47 -0400

Dear Patricia,

Thank you for the explanation.

I understand that the decision to present the results as mean and SD
is not yours.  If, however, the display will show mean and SD for
medstable and, separately, mean and SD for durofstay, I find it
difficult to see how such a display would be appropriate without
further analysis.  The main problem is that it would ignore the
connection between those variables' values for the same patients.  The
differences within the individual patients are often the most
important part of the difference between the variables, so one needs a
strong justification for not looking at them.  To see the "whole
effect," you need to clear away the variation among patients.  Another
shortcoming is that the SD isn't a very good summary of variation when
the data are substantially skewed.  For some analyses it is helpful to
transform such variables, by using the logarithm or perhaps the
reciprocal.

I'm not sure how one determines "that people stay longer in hospital
as actually needed," but a scatterplot is likely to be important.  A
plot of medstable versus (durofstay MINUS medstable) would show
whether medstable is associated with the length of stay before the
patient achieves medical stability.

David Hoaglin

On Wed, Apr 4, 2012 at 7:12 AM, Patricia Biedermann
<pati.biedermann@gmail.com> wrote:
> Dear David,
>
> Both variables are positive (right) skewed) and the variables come from the same patients. We want to see the difference between the two variables (that people stay longer in hospital as actually needed). The difference of each person is not so important now....we want to see a whole effect.
>
> The results should be presented in mean and SD...(was not my decision...I just have to do the graphs)

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