Sorry, I was imprecise.
According to Bill Whittle (who got his information from Heather MacDonald, the WSJ reporter who investigated this) it should say: “Over the last ten years, a police officer is 18 times more likely to be killed by a black assailant, than an unarmed black man is to be killed by a cop.”
(I had to go back and watch the video by Bill Whittle that summarizes Ms. MacDonald’s findings)
I couldn't get by the WSJ pay wall, or I would have found the answer on my own.
Thanks for clearing it up.