Alice and Kathleen, thank you for your responses.

Neither am I aware of any actual data, just people throwing out numbers in various places at various times.  I have heard or read somewhere recently, someone in the know (but I can't remember who, where or when), saying something to the effect of "we used to think it was an extremely small percentage, but have come to realize it is a higher percentage than we  thought."

 Just look at the wide divergence in the two statements you cite, Alice - 1 of 20 (5%) to 1 of 2000.

I agree that the number will differ widely depending on the area of the
 world we are talking about, and the amount of medical technology 
available. I would expect to see a much lower rate of inability than in
 the US, for instance, in areas where the community cannot spend a 
lot of time and/or money on helping moms get pregnant and stay
 pregnant, or where there is not so much surgical intervention for 
cosmetic reasons, or  where young or childbearing women either do 
not survive, or do not go on to have children (are there any such, any
 more), 

Lately I have been using the following, rather than citing meaningless, 
misleading, or erroneous numbers--   "Even if one in ten..." and then go on to discuss my premise.
              
for example:

         "Even if as many as one in ten dyads CAN'T breast feed,
         for whatever reason, still that leaves nine in ten that CAN.
          And 90% is a a far greater precentage than the the  75%, minimum, we would like to see."

I chose the 1 in 10, because it might mollify all those  I-tried-to-but readers, enough so that they will read or hear the rest
of what I have to say.  I would like to give an even smaller (greater?)
ratio -- like 1 in 20 or 1 in 50, but I can just see a roomful of women where  4 of every 20 stand  up, each one  fully certain that she is the ONE who couldn't breastfeed.

Sincerely, Chanita, San Francisco