Re: Confounders and Coincidences

[epirad@mchsi.com]

Jerry, a good example of what Dr. Raabe is referring to -  



Am J Epidemiol 1992 Jan 1;135(1):85-95   



Effects of nondifferential exposure misclassification in ecologic studies.



Brenner H, Savitz DA, Jockel KH, Greenland S.



Unit of Epidemiology, University of Ulm, Germany.



Although many authors have argued against inferring individual-level exposure-

disease relations from ecologic data because of the potential "ecological 

fallacy." the availability of data from diverse populations promotes the 

continued use of this rapid and inexpensive study design. In ecologic studies, 

the exposure status of groups is often defined by the proportion of individuals 

exposed. In these studies, nondifferential exposure misclassification of 

individuals is shown to produce overestimation of exposure-disease associations 

that may be extreme when the ecologically derived rate ratios are applied to 

individuals. This overestimation contrasts with the bias toward the null 

resulting from nondifferential misclassification of a binary exposure in 

epidemiologic studies conducted at the individual level. Given the magnitude of 

the potential bias from nondifferential exposure misclassification and other 

sources, quantitative estimates of individual-level rate ratios from ecologic 

data should be interpreted with extreme caution.



R. William Field, Ph.D.

Community of Science: http://myprofile.cos.com/Fieldrw

> 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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