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Re: st: Re: advice re: "intervening" variable


From   Richard Goldstein <richgold@ix.netcom.com>
To   statalist@hsphsun2.harvard.edu
Subject   Re: st: Re: advice re: "intervening" variable
Date   Mon, 05 Mar 2007 11:58:11 -0500

Thanks to Sergiy and Austin:

Sergiy:

In this case, at least, it works as I stated because the researchers
force it to work this way -- they give each S a drug that directly
affects blood pressure; the change in blood pressure affects
vessel diameter and, then, heart rate

Thanks to both re: citations

Rich

Sergiy Radyakin wrote:
Hello Richard,

Google picture search --> "structural model" will give you a lot of examples.
However "intervening" variable is the one which usually reflects a Concept, like "hunger" or "fear" (lots of examples from the area of psychology).

E.g. here you will find a model of impulse-buying behaviour:
http://emeraldinsight.com/Insight/ViewContentServlet?Filename=Published/EmeraldFullTextArticle/Articles/2840100404.html

While "Fashion involvment" and "Impulse buying" are quite real, "positive emotion" is rather hypothesized.

Your "diameter of blood vessel" seems to be quite a real variable though.
I am not a doctor, but I thought it works the other way around:
one smokes --> diameter decreases --> pressure increases --> heart rate increases --> one dies ?

Another chain:
"Moreover, The nicotine in cigarettes and other tobacco products causes your blood vessels to constrict and your heart to beat faster, which temporarily raises your blood pressure. "
is described here: http://www.highbloodpressuremed.com/smoking-and-high-blood-pressure.html

I wonder how do you establish causality in this case?

----
An example from economics (Student Achievement and National Economic
Growth, Nov 2006): http://www.journals.uchicago.edu/AJE/journal/issues/v113n1/113101/113101.web.pdf


Regards, Sergiy



----- Original Message ----- From: "Richard Goldstein" <richgold@ix.netcom.com>
To: "statalist" <statalist@hsphsun2.harvard.edu>
Sent: Monday, March 05, 2007 3:57 PM
Subject: st: advice re: "intervening" variable



Hi all:

This is more a stat question that a Stata question.

I have a system of 3 variables where one variable is in between,
in time and physiology, the other two variables:

blood pressure -> diameter of blood vessel -> heart rate

That is, a change in blood pressure "causes" some change in
the diameter of the blood vessel which in turn "causes"
some change in heart rate (actually in "RRI" which is,
basically, the inverse of heart rate).

I have never come across this situation before, but I believe
that several substantive disciplines do have such situations.

Actually, I have found a fair amount of literature in
psychology; a recent overview is MacKinnon, DP, AJ Fairchild,
and MS Fritz (2007), "Mediation Analysis", _Annual Review of
Psychology_, 58: 593-614

I believe that other disciplines might also see such
situations, e.g., economics and epidemiology, but have
been unable to find any literature.

So, is there literature on this in disciplines other than
psychology? If so, any citations, esp. overviews, would
be greatly appreciated (regardless of whether the cite is
to ariticles or books).

Thanks,

Rich

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