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st: RE: Re: z-score diff plots

From   "Lachenbruch, Peter" <>
To   "" <>
Subject   st: RE: Re: z-score diff plots
Date   Thu, 11 Apr 2013 17:25:53 +0000

sounds like there might be two approaches here:
ignore the covariate  and do a regression
do the regression with the covariate fixed at the mean value in the first group (or even get the values)
and compare the intercepts.  Probably should use an interaction of group and coavariate

Peter A. Lachenbruch,
Professor (retired)
From: [] on behalf of Joseph Coveney []
Sent: Wednesday, April 10, 2013 7:40 PM
Subject: st: Re: z-score diff plots

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

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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