I do remember having read that a lot of law enforcement agencies don't collect, or collect in a way that makes it hard to tabulate shootings by officers- but a) I don't have a cite for that, it was a while ago, and b) that's also up to individual enforcement agencies, not federal.
- https://en.wikipedia.org/wiki/Dickey_Amendment_(1996)
- The Congressman Who Restricted Gun Violence Research Has Regrets: http://www.huffingtonpost.com/entry/jay-dickey-gun-violence-...
- The ban has supposedly been lifted: https://www.washingtonpost.com/news/storyline/wp/2015/01/14/...
- Some more history: http://www.apa.org/science/about/psa/2013/02/gun-violence.as...
- some background: http://www.latimes.com/business/hiltzik/la-fi-hiltzik-gun-re...
And I love this entry on a blog site (Forbes): Why The Centers For Disease Control Should Not Receive Gun Research Funding: https://www.forbes.com/sites/larrybell/2013/02/12/why-the-ce...
The reasoning? "There was a very good reason for the gun violence research funding ban. Virtually all of the scores of CDC-funded firearms studies conducted since 1985 had reached conclusions favoring stricter gun control. "
You can have gun rights and gun control you know..