I think it is very naive to think that the CFA doesnt put out exams that very in difficulty. It has been speculated that the Institute uses the "modified angoff" method in order to adjust the pass rates and to correct for differences in the degree of difficulty between any given exam. However, this is a grading method that is done after the fact. So in other words, it is very possible to have a December exam that was much more diificult than a June exam. In addition, many will tell you that the December exam is much more difficult, historically speaking. Now, whether this is because the CFA is puposefully creating this way is a different story....