Oh, look at the smart guy making assumptions about peoples intelligence because they asked for facts to back up a claim. Also, your brilliant google stat (No source, I noticed) says "contributed." 

So does that mean they were also drunk, on coke, or meth? I'm guessing it does. What say you, professor? Or, what say Google I should say. Does it still mean weed causes accidents if you're also drunk over the legal limit? Or should we just blame all of that on marijuana anyway? 

If *you* actually do more research you may find that it's hard to measure what the effects are of weed on driving because it is being done in conjunction with other substances. It's also difficult to test and determine an exact level of impairment. Further, you may not have smoked in a week, yet a drug test will come back positive because of how long it stays in your system. So you could be completely sober and test positive for marijuana. (I can be a jerk on the internet too. It's fun!)