Re: Recommendation to resolve Cohen's ecologic study questions

Dr. Cohen,

Even the concept of collective dose is based on exposure AND

demographics. Use of collective dose assumes that you have good

information on demographics. While the level of demographic information is

not always what it should be in collective dose studies, it nonetheless is

an assumption of using collective dose. If you want to improve your

ecologic analyses, you need more information concerning within county

demographic correlations.

The explanation is simply that you have group level confounding that you

have not accounted for. Smoking (among other factors) confounds your radon

covariate at the regional level, but most of the smoking variability occurs

within counties rather than between counties. Therefore, as suggested in

Guthrie's paper (which I faxed to you), you need county level population

incidence data and covariate data from a sample survey. As we pointed out

before, in order to explain your findings you will likely need more data

than is available from existing published sources.

Repeating, the specific cause of your findings is the failure to account

for intercounty smoking covariates in your data. I understand you have not

considered these before because of lack of that data. One method to get at

these inter county relationships would be the suggestions in Guthrie's

paper, but obviously you are surely free to use any method you would like.

Regards, Bill Field

Information on the Burlington IAAP study can found at:

http://www.public-health.uiowa.edu/baecps

R. William Field, M.S., Ph.D.

College of Public Health

Department of Epidemiology

Department of Occupational and Environmental Health

N222 Oakdale Hall

University of Iowa

Iowa City, Iowa 52242

319-335-4413 (phone)

319-335-4748 (fax)

mailto:bill-field@uiowa.edu

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