There are annual reports and statements that have been made in public, but there is very little systematic research. I must say it is also the case in most other countries. There are very few cases.
There are some cases, such as the federal marshal program in the U.S. and others that have been subjected to a fairly detailed review, but typically these programs are covered by some kind of veil of secrecy, which is partly justified. Obviously, you need to keep these operations confidential and secret to a certain extent, but it's a level of secrecy that is not justified. It is quite possible to review those programs in a more open and transparent way without compromising anybody's security.