[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Recommendation to resolve Cohen's ecologic study questions



Dr. Cohen,

Here is my specific recommendation.  If you are really interested in using your ecologic data and getting at the potential sources of your bias, you need to identify what inter county adjustments need to be made by using more innovative methods.  Possibly those suggested in: Guthrie, KA and Sheppard, L, Overcoming biases and misconceptions in ecological studies, J.R. Statist. Soc., volume 164, pp 141-154, 2001.

In your past stratifications, you have confused individual level confounding with group level confounding.  You can not hope to correct for bias in your ecologic model by using stratification based on individual level model confounders when your model has non-linear and non-additive effects.  Therefore, if you hope to explain your findings, you need to use aggregate level confounder models possibly using the aggregate data approach as specified by Guthrie and Sheppard.  However, this will require some data collection on your part. 

I would be happy to fax you the paper if you are interested.  I wish you good luck.

Regards, Bill Field


Regards, Bill Field

R. William Field, M.S, Ph.D.
College of Public Health
Research Scientist - Department of Epidemiology
Adjunct Professor - Department of Occupational and Environmental Health
Graduate Faculty - College of Public Health
N222 Oakdale Hall
University of Iowa
Iowa City, Iowa  52242

319-335-4413 (phone)
319-335-4748 (fax)
mailto:bill-field@uiowa.edu

At 12:48 PM 01/22/2002 -0500, BERNARD L COHEN wrote:
> 2) They continue to say that cross-level bias and inter county variability
> caused your findings.  Do you really have the data to show this is not the
> case?

        --I need a specific example -- see above. If a specific example is
offered, it is up to me to supply the data required.

> My most important question about the Field and Smith paper:  Are adjustments
> made using aggregate data (smoking, education, etc.)usually used to adjust
> for confounding at the individual level - sufficient for use in adjusting at
> the county level?

        --I do not "adjust" my data for anything. I treat confounding by
my method of stratification which is very much superior.

>  From reading their papers they say you may never find
> your answer because your data are lacking.  Can you really say you have
> tested all the possibilities if you do not have the data you need to adjust
> for aggregate confounding?

        --Providing the data is my problem. What I need is a
specific suggestion for which data are needed.
************************************************************************ You are currently subscribed to the Radsafe mailing list. To unsubscribe, send an e-mail to Majordomo@list.vanderbilt.edu Put the text "unsubscribe radsafe" (no quote marks) in the body of the e-mail, with no subject line. You can view the Radsafe archives at http://www.vanderbilt.edu/radsafe/