Comment by fiatmoney

Those numbers conflate "ever sold" with "sold in the last N days", and yearly vs. weekly usage rates. For regular usage (which would be expected to track sales, and possession) the numbers are substantially higher for blacks.

http://slatestarcodex.com/2014/11/25/race-and-justice-much-m...

Is a good meta-analysis, which on this particular data point leads to:

http://www.bjs.gov/content/pub/pdf/rdusda.pdf

And in the OP's substantive point about "violent crimes", the FBI's crime stats prove them definitively correct.