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Subject:
From:
Susan Burger <[log in to unmask]>
Reply To:
Lactation Information and Discussion <[log in to unmask]>
Date:
Fri, 23 May 2008 07:58:39 -0400
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Dear all:

Reverse causality is one of the most common flaws in the interpretation of study results.  
Breastfeeding research is particularly prone to this because you simply cannot randomly 
assign the "treatment".  You can randomly assign large population groups to a treatment 
within a clinic or hospital or community --- but your sample size is NOT the number of 
people in the clinic, hospital or community, it is the number of clincs, hospitals or 
communities.  Essentially a "nested" design that requires a completely different analysis.

So, given that most studies are "association" studies --- they are particularly prone to 
reverse causality.  My clinical observations suggest to me that the issue of food 
consumption for an allergic child is one of reverse causality.  Every single allergic child I 
have ever seen has a great deal of difficulty accepting solids.

The most stunning humiliation of a graduate student I ever saw was over the 
breastfeeding and allergy issue.  The authors of the study, the reviewers of the journal, 
the poor graduate student that chose the study to review for our big seminar that we all 
had to do in front of our professors and our peers missed the results. They so expected 
breastfeeding to reduce allergy symptoms that they didn't even spot that the results 
showed the exact opposite.  There were more symptoms in the breastfed infants.  It is 
very hard to challenge our expectations.  My professor had an amazing talent for spotting 
flaws like this and the poor graduate student was royally dissected by him.  I was so 
fearful of ever having that happened that I ALWAYS check the numbers in the tables 
against what the authors think they saw.

At the time, we thought that the reason why there were more "symptoms" was that 
breastfeeding mothers spotted them sooner because of close proximity.  A similar issue 
crops up with vitamin A deficiency.  Those treated sometimes have more "symptoms".  A 
deeper look eventually revealed that there was less severe respiratory disease among 
those who were given a vitamin A supplement, but some of the less severe symptoms 
were increased.  Allergies are very complex.

Best, Susan Burger

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