Jennifer part 2

Jennifer is now at the new traffic junction which reported a lot of accidents. She decided to make another count.

"Hmm.... 0.4% accident when turning left, 1.1% if going straight, 0.05 when turning right," she noted and wondered, "This is confounding!" Comparing to part 1, why is it confounding?

She thinks about the theories that she had known, and thought, "Vision theories can explains," continuing, "There is a mountain on the left side of the road, which blocks out sunlight most time of the day. The lack of light is probably the culprit." Is vision theory appropriate?

She took some readings of illumination and found the right side of the road is indeed brighter. She did statistics and found correlation between brightness and accident is positive at 95% confidence. Is this the result we wanted?