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RE: st: trend in ORs across ordered levels of a 3rd variable

From   "Visintainer, Paul" <PAUL_VISINTAINER@NYMC.EDU>
To   <>
Subject   RE: st: trend in ORs across ordered levels of a 3rd variable
Date   Tue, 22 Apr 2008 10:02:04 -0400

Thanks Maarten, Peter, and Berthold.  I arrived at a similar
conclusion--addressing the problem through logistic regression.  But,
I'm interested in Maarten's and Berthold's use of -suest-, which, from
what I gather, is the Chow test (or something like it), right?

Maarten, your model tested the interaction term in the logit.  Am I
right to assume that, in this situation, the Chow test and the logit
test of the interaction term are accomplishing similar goals?



Paul F. Visintainer, PhD
Department of Epidemiology and Biostatistics
School of Public Health
New York Medical College
PH: (914) 594-4804
FX: (914) 594-4853
-----Original Message-----
[] On Behalf Of Maarten buis
Sent: Tuesday, April 22, 2008 8:23 AM
Subject: RE: st: trend in ORs across ordered levels of a 3rd variable

--- Visintainer, Paul asked:
> What I wanted to know is whether we can detect a linear pattern of
> the ORs over levels of the confounder (which, to me, looks like a
> specific type of interaction)

--- Peter A. Lachenbruch answered:
> This sounds like a task for logistic regression using the confounder
> and the risk factor.  If you want to see if there's effect
> modification, use the product of the risk factor and confounder.  You
> may want to categorize these variables.

--- "Berthold Hoppe" responded:
> The problem seems to be similiar to one I am actually faced with.
> Have you tried an analyses like this:
> logit death consc if sex==0
> est store A
> logit death consc if sex==1
> est store B
> suest A B
> test [A]consc=[B]consc

There is no need to use -suest-, this is just an interaction term:

*----------- begin example -------------------
sysuse nlsw88, clear
gen byte grade3 = cond(grade <  12, 1, ///
                  cond(grade == 12, 2, 3)) ///
                  if grade < .

gen southXgrade3 = south*grade3
logit marr south grade3 southXgrade3

logit marr grade3 if south == 1
est store A
logit marr grade3 if south == 0
est store B

suest A B
test [A]grade3=[B]grade3
*---------------- end example ----------------
(For more on how to use examples I sent to the Statalist, see )

However, the propper interpretation of these results is a very very
tricky issue regardless of whether you estimate this using an
interaction term or -suest- and you will want to take a good look at:

There is also a second problem with this approach which is among others
discussed in this post: 

Hope this helps,

Maarten L. Buis
Department of Social Research Methodology
Vrije Universiteit Amsterdam
Boelelaan 1081
1081 HV Amsterdam
The Netherlands

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