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 *********************************************** Archives: http://community.lsoft.com/archives/LACTNET.html To reach list owners: [log in to unmask] Mail all list management commands to: [log in to unmask] COMMANDS: 1. To temporarily stop your subscription write in the body of an email: set lactnet nomail 2. To start it again: set lactnet mail 3. To unsubscribe: unsubscribe lactnet 4. To get a comprehensive list of rules and directions: get lactnet welcome