According to Illinois law, a crosswalk is the part of the road- way at an intersection that is in line with at least one sidewalk. A crosswalk need not have markings on the road. In 2010, a law was passed in Illinois that requires motorists to come to a complete stop for pedestrians in crosswalks. Researchers wanted to determine whether motorists are more likely to follow the “Must Stop” law for marked crosswalks than for unmarked ones. A trial consisted of a researcher standing with one foot in the street, which the study claims is a clear indication that the researcher wanted to cross the crosswalk. Data was collected at 52 sites—some marked crosswalks and some unmarked—throughout Chicago. At each site, 4 trials were completed. The study found that motorists are more likely to follow the Must Stop law at marked crosswalks than at un- marked ones.
a. Is the study an experiment or an observational study? Explain.
b. Describe the sample and the population.
c. What are the explanatory and response variables?
d. What is the conclusion of the study? Does it have to do with causality or only association? Explain.
e. Can we assume the conclusion is also true for motorists in Prairie City, Illinois, which has population 379 and is surrounded by farmland? Explain.