The CFA Institute publishes its historic pass rates on their website.
There is some interesting data that can be found.
1. The total number of CFA candidates that have taken the CFA Level I exam from 1963 to 2013 was 1,878,714.
2. The total number of CFA candidates that have taken the CFA Level I exam from 2004 to 2013 was 1,307,349.