On July 2, 2006, the Forest Park Police Department set up a sobriety checkpoint in Forest Park, Illinois. For the first part of the evening—when traffic was heavier—the police stopped every fourth car. Later, when the traffic was lighter, the police stopped every third and fourth car.
a. What type of sampling method did the police use when the traffic was heavier? Explain.
b. Later in the evening—when traffic was lighter—the police stopped every third and fourth car. Is this systematic sampling? Explain.
c. Describe how the police could have performed systematic sampling when traffic was lighter and still stopped the same number of cars.