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Topic: confounding: a recent example
Replies: 1   Last Post: Nov 27, 1996 10:27 AM

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Posts: 144
Registered: 12/6/04
confounding: a recent example
Posted: Nov 27, 1996 9:39 AM
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There are good discussions and/or examples of "confounding" in some of
the statistics textbooks in current use (e.g., Rossman, Moore's BPS).
Nevertheless, it doesn't seem to be easy to make this clear to
students--at least not in a single encounter.

Moore & McCabe's IPS shows on p.201 a nice diagram that helps distinguish
among these situations:
(a) changes in x cause changes in y
(b) x is correlated with y because each is affected by changes in a
lurking variable z
(c) the effect of x on y is unclear due to the existence of a lurking
(confounding) variable z that causes changes in y
I think the diagram usefully augments the words and examples we use, and
I wish this diagram had not be eliminated in BPS.

Anyway, sometimes a current example can help. There was a neat one in an
AP release that appeared in my local newspaper on Nov. 21; so it probably
appeared in many other newspapers around the country about the same

Briefly, the article reminds readers that it has long been known that
American blacks suffer from cardiovascular diseases at higher rates than
American whites. But it now appears that the difference was not race; it
was place! That is, the higher rates of American blacks are almost
entirely due to higher rates among southern blacks. Norhern blacks and
Caribbean blacks did not have the same high rates as southern blacks.

Unfortunately, the study was not able to compare southern whites with
northern whites; so the study's results are not yet conclusive.

I think this could make an easy-to-understand classroom example. If you
can't find the article in a local newspaper, my copy says that the study
"was published in Thursday's issue of the New England Journal of
Medicine." Since Nov. 21 was a Thursday, I supppose that could mean the
Nov. 21 issue of NEJM; or maybe Nov. 14. Either way, it shouldn't be
hard to find.

Bruce King
Department of Mathematics and Computer Science
Western Connecticut State University
181 White Street
Danbury, CT 06810

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