Re: Concrete Ecologic Example Myth

[Kai Kaletsch <eic@shaw.ca>]

Bill,



I think you are confusing trying to establish a dose response relationship

from ecological data with testing a particular theory against an ecological

observation. These issues are not limited to epidemiology. It tends to be

difficult (impossible?) to formulate a theory of how small things interact

by just looking at the end result of the interaction, but any valid theory

must still be compatible with the observation.



If I look at Mars and it looks red, that is not proof that Mars is populated

by a bunch of compulsive Martians who go around painting everything red.

However, if you have a theory that states that Mars is populated by a bunch

of compulsive Martians who go around painting everything green, then my red

observation is a problem for your theory. That doesn't mean your theory is

wrong, but it would sure help if you could come up with an explanation that

reconciles your theory with my observation. (e.g. Martians have wives that

go around covering the green paint up with red blankets.)



To me, no one has come up with an explanation that makes LNT compatible with

the ecological observation. Until that happens, I can't accept LNT as a

valid scientific theory. (Using LNT as a basis of regulation is a different

story.)



You state that many examples have been given on how Dr. Cohen's data can be

biased. I don't recall any that seem reasonable to me. All I need is one

NUMERICAL example. Put 1600 hypothetical counties on a spreadsheet. Put in

some confounders (Martian wives) and reproduce the ecological observation.

(You correctly state that it may be impossible to IDENTIFY empirical sources

of ecologic bias from aggregate data alone, but that should not stop you

from POSTULATING them.)



Kai



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

From: <epirad@mchsi.com>

To: "Kai Kaletsch" <eic@shaw.ca>

Cc: "BERNARD L COHEN" <blc+@PITT.EDU>; <radsafe@list.vanderbilt.edu>

Sent: Friday, June 20, 2003 12:54 PM

Subject: Concrete Ecologic Example Myth





> Kai,

>

> I know we have gone through discussions about the limitations of ecologic

> studies many times but there are some points that a few radsafers continue

to

> miss.

>

> You suggested the other day putting an upper limit on the error from an

> ecologic study.  Unfortuantely, this is not easy to do since the error in

> ecologic studies is unbounded.

>

> Others problems to keep in mind -

>

> 1) It is not possible to identify empirical sources of ecologic bias from

> aggregate data alone. Researchers must rely on prior knowledge of

intergroup

> variation in the distribution of other risk factors and effect modifiers.

> We don't know this inter group variation for Dr. Cohen's data nor has he

> adjusted for it.

>

> 2) Factors responsible for ecologic bias may not be confounders or effect

> modifiers at the individual level and that identifying the bias is even

more

> difficult because factors may not even "appear" to be confounders or

modifiers

> at the ecologic level.

>

> 3) Ecologic biases can even reverse the direction of an observed

association,

> especially when the range of average exposure levels across groups is

small or

> the exposure under study is not a strong risk factor regardless even if

you are

> using an ecologic study to test the LNT.

>

> 4) If cross level bias is occurring (which we know it is), ecologic data

can

> not be successfully used to adjust for ecologic bias.

>

> Many examples have been given on how Dr. Cohen's data can be biased and

since

> Cohen will use his own faulty data to test the "concrete" example;

providing

> a "concrete" example is doing no more than providing an explanation Cohen

will

> use his own faulty data to negate.  So, the circle will never end.

> > Friends,

>

> > We are all aware that ecological studies have some limitations - these

issues have been discussed (some would say ad

> > infinitum) on this board and elsewhere.

>

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