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Re: st: Re: z-score diff plots


From   Nick Cox <njcoxstata@gmail.com>
To   "statalist@hsphsun2.harvard.edu" <statalist@hsphsun2.harvard.edu>
Subject   Re: st: Re: z-score diff plots
Date   Thu, 11 Apr 2013 15:55:41 +0100

Plotting difference against mean is a standard plot for many people.

It is a relative of  the principle that it is helpful to plot residual
against fitted.

Plotting some difference against a third variable might similarly be
useful. It is a bit like the standard practice of plotting residuals
from some model against a predictor not in the model.

The question is does it work, that is, can you see a pattern?

There are some general references in

SJ-4-3  gr0005  . . . . .  Speaking Stata: Graphing agreement and disagreement
        . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  N. J. Cox
        Q3/04   SJ 4(3):329--349                                 (no commands)
        how to select the right graph to portray comparison or
        assessment of agreement or disagreement between data
        measured on identical scales

.pdf accessible via http://www.stata-journal.com/article.html?article=gr0005

Nick
njcoxstata@gmail.com


On 11 April 2013 15:24, Nikos Kakouros <nkakouros@gmail.com> wrote:
> Thanks, Joseph.
> I was hoping to have a single graph demonstrating the interaction
> between the three variables.
> I wonder what anyone thought of the proposed idea of plotting the
> z-score difference between the two tests against the interacting
> variable...
> KR
> Nikos
>
> On Wed, Apr 10, 2013 at 10:40 PM, Joseph Coveney <stajc2@gmail.com> wrote:
>> Nikos Kakouros wrote:
>>
>> I'd like to first apologize upfront for the lack of specificity in my
>> question - please be sensitive to my lack of experience with Stata. :)
>>
>> I have two tests that are meant to measure the same thing (blood
>> thickness) but with totally different units. On the whole they
>> correlate well (patients with thick blood have higher values on both
>> measurements), but the first test is affected (on univariate analysis)
>> by another blood parameter but the second test is not. Their
>> correlation is, therefore, dependent on the third parameter.
>>
>> I would appreciate on comments/advice on how to best visually show
>> this relationship in Stata. I was thinking the following: convert all
>> measurements to z-scores and depict the difference in z-score for the
>> two measurements at different values (y axis) vs the value of the
>> third variable that affects one of the tests more than the other
>> (x-axis).
>>
>> Is anyone familiar with such a visualization?
>>
>> --------------------------------------------------------------------------------
>>
>> I'm not familiar with it.  Would a scatterplot matrix (SPLOM) help?
>> (See -help graph matrix-.)
>>
>> Joseph Coveney
>>
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