Marijuana and traffic accidents (1.1) Researchers in New Zealand interviewed 907 drivers at age 21.

They had data on traffic accidents and they asked the drivers about marijuana use. Here are data on the numbers of accidents caused by these drivers at age 19, broken down by marijuana use at the same age:29 Marijuana use per year Never 1–10 times 11–50 times 51 • times Drivers 452 229 70 156 Accidents caused 59 36 15 50

(a) Make a graph that displays the accident rate for each class. Is there evidence of an association between marijuana use and traffic accidents?

(b) Explain why we can’t conclude that marijuana use causes accidents.