Chapter 1, Problem 15E

(Exercises 19–26) For each description of data, identify Who and What were investigated and the Population of interest.

21. Bicycle safety Ian Walker, a psychologist at the University of Bath, wondered whether drivers treat bicycle riders differently when they wear helmets. He rigged his bicycle with an ultrasonic sensor that could measure how close each car was that passed him. He then rode on alternating days with and without a helmet. Out of 2500 cars passing him, he found that when he wore his helmet, motorists passed 3.35 inches closer to him, on average, than when his head was bare. (Source: NY Times, Dec. 10, 2006)