Re: Ecologic versus Case-Control Studies, revisited

[Bernard L Cohen <blc+@pitt.edu>]

On Fri, 27 Feb 1998, R. William Field wrote:
> BF Response ---- The ecologic study is not more powerful because of the non
> quantifiable biases within the data set, you have no idea what types of
> cross-level biases have been introduced.  Again, what Dr. Cohen has is a
> large data set, this does not make a study more powerful.

	--If this is the problem you imply that it is, surely you can make
up a not implausible example. In the 3 years since my paper was published,
and despite the large monetary rewards offered, no one has done this. Your
example does not have to be true, as long as it is not implausible. It
seems to me that the time has come for those who cry "cross level bias" to
put up or shut up.


> BF RESPONSE - It is very difficult to control confounding on the ecologic
> or aggregate level.  Sometimes things that may not even be (or appear to
> be) confounders on the individual level become confounders on the aggregate
> level.  It also does not make a study more valid by increasing the number
> of adjustments you do.  A study with 1000 attempted adjustments has no more
> validity than a study with 100 adjustments.  If you actually knew what the
> confounder is, only 1 adjustment would be needed.  In ecologic studies the
> confounders are generally non-linear and not apparent, which makes
> adjustments almost impossible.

	--Non-linearity is not a problem in my procedures. An unknown
confounder can invalidate any epidemiological study, and none have
considered as many possible confounders as mine. If the problem is as you
say, why can't you make up a not implausible example and claim the reward,
and also settle a large issue in the scientific community?

> 
> Two last thoughts on ecologic studies.
> 
> 1) Case-control studies follow-up the findings of ecologic studies.  I have
> never seen it go the other way.  There must be a reason for this.
> Case-control studies are analytical in nature, while ecologic studies are
> hypotheses generating.

	--Is this an "article of faith", or can you prove it.

> 
> 2) Dr. Cohen's  Study is not the only large ecologic study that has found
> paradoxical findings.  Absurd paradoxical findings have been found in other
> ecologic studies surveying numerous countries.  For example, a huge
> ecologic study in Europe has found that high blood pressure protects you
> from having a stroke.  Obviously this is a ludicrous finding.  But, that is
> what they found using a large ecologic study.  The European study used
> "powerful and advanced statistics" , but still found a paradoxical rather
> non believable finding.
> 
> Dr. Cohen has been unable to explain how his ecologic study can produce
> false results.  He asks others to explain his findings.  Dr. Cohen has
> stated he can explain the false results of any other ecologic study (other
> than his own).  He has frequently offered in the past to show how other
> ecologic studies can produce false results.  I challenge Dr. Muckerheide or
> Dr. Cohen to explain the paradoxical findings published in the study by
> Menotti et al., European Journal of Epidemiology 13: 379-386, 1997.  

	--If you can give me some reason to believe that this would be
publishable, I would be glad to accept this challenge. I am quite sure
that a challenge to my paper would be publishable, and in addition, there
is a large monetary reward.
	I will take a fast look at the Menotti paper anyhow and maybe I
can reply briefly to your challenge without much trouble.

> 
> I do not see this whole issue on the validity of ecologic study as a debate
> between Epidemiologist and Health Physicist.  While I have "recent"


	--The issue here is "the scientific method", according to which
all data must be explainable in a not implausible way. Anyone claiming to
be a scientist must abide by that rule. Why do some people feel that they
are exempted from it by expressing dogmatic "articles of faith"?