For the following situation, identify the explanatory and response variable. Then discuss what reservations (think cautions) you might have about the results of the experiment. Asking “What if…” type questions may help. Do the high, centered brake lights (which have been required on all U. S. cars since 1986) really reduce the frequency of rear-end collisions? Randomized comparative experiments with fleets of rental and business cars, done before the lights were required, showed that the third brake light reduced rear-end collisions by as much as 50%. After the lights were required the drop was only 5%.