I have been wondering about this type distribution issue quite a lot. Socionics.com claims that it is almost impossible to say anything with any degree of reliability:

You have to be careful with the type distribution statistics, especially the one that is based on "total population". Firstly, there is no reliable psychometric instrument of today that can stand up to such a challenge. Secondly, if statistics is not accompanied by the fact sheet on how, where and when it was gathered, it has no scientific value
http://www.socionics.com/advan/qa.htm?1119823774

It is indeed a sad statement of the current state of progress of socionics that there is still no fully reliable method of determining the sociotype. Nevertheless presuming that a combination of tests and interviews by experienced socionists should be able to determine the correct type with fairly high confidence and since making statistically reliable predictions based on small representative samples is a scientifically respectable and common practise which has been studied in great detail, I think it should be fully possible to try to empirically study the distribution of the types even in "the total population". Of course getting a sufficiently large statistically representative sample of people to analyze would probably take a fair amount of money, time and resources that may not be currently available. I think it is a question that would deserve serious attention though.

There are various, often contradictory, claims about the distribution of types, and what inspired me to write this post was this article (well worth reading) published online by the International Socionics Insitute that, at least as far as I can understand it, seems to imply that there should be an equal number of representatives of both types of each duality pair, or duality diad. This is manifestly not what pretty much all available MBTI type distribution statistics show. What I find puzzling, but the article does not address, is why should there be an equal number of members of the both types of each duality pair? I would like to know if there are any socionics studies that confirm this seeming peculiarity, or what are the theoretical considerations that would cause this? Any thoughts anyone?