One thing that is difficult about studies doing logistic regressions is 
that when two variables that they include in the analysis are highly 
linked, then one or both can end up getting kicked out of the model as not 
being "independent" variables, though it may be that both are 
significant.  So if babies who are breastfed also tend to have good 
prenatal care, then if prenatal care is significant, then breastfeeding 
may get kicked out of the model.  Breastfeeding may still have an 
influence, but teasing that out from the influence of prenatal care may 
require much larger numbers than they would have had.

(And thanks Tarah for the analysis of the Peds article -- spoken like 
another 

Shannon McElearney, MD, MS
Dept of Surgery
UVA
another eventual breastfeeding researcher, only from the surgery side (is 
there such a thing?  hopefully, by the time I'm done!)

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