Re: Confounders and Coincidences

["Jerry Cohen" <jjcohen@PRODIGY.NET>]

Otto,

    Even in epidemiologic studies, confounding factors can affect results.

For example, both the cause and effect under study may have a common

cause. Suppose for some unknown reason (genetic or otherwise), those

individuals who are prone to getting lung cancer, also harbor a propensity

toward smoking. This would account for the observed positive correlation

between smoking and cancer. Even if these individuals somehow overcome

their tendency to smoke, they would  still have an increased likelihood of

lung cancer. Granted, this example may be implausible, but it is not

impossible.





----- Original Message -----

From: Otto G. Raabe <ograabe@ucdavis.edu>

To: Jerry Cohen <jjcohen@prodigy.net>

Cc: internet RADSAFE <radsafe@list.vanderbilt.edu>

Sent: Monday, May 05, 2003 6:50 AM

Subject: Re: Confounders and Coincidences





> May 5, 2003

> Davis, CA

>

> Dear Jerry:

>

> I agree with you for the most part, but unknown confounders are not the

> problem in epidemiological studies that they are in ecological studies. I

> cannot agree with your blanket statement that "...all epidemiologic

studies

> up to and including those relating smoking to

> lung cancer could be discounted on the basis of possible unknown

> confounding factors...." The key difference is that the exposure of each

> individual in an epidemiological study is evaluated and the statistical

> probability of erroneous results is also evaluated. In an ecological study

> we have no way of knowing the dose to any particular person, nor do we

know

> the chance that the results are spurious even if they are not.

>

> Sincerely,

>

> Otto

>

> **********************************************

> Prof. Otto G. Raabe, Ph.D., CHP

> Center for Health & the Environment

> (Street Address: Bldg. 3792, Old Davis Road)

> University of California, Davis, CA 95616

> E-Mail: ograabe@ucdavis.edu

> Phone: (530) 752-7754   FAX: (530) 758-6140

> ***********************************************



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