What are the observational/experimental units?

Researchers from the University of California, Berkeley wondered whether upper-class individuals behave more unethically than lower-class individuals. To further investigate this question, they studied behaviors of drivers in different makes and models of cars. The cars were a surrogate measure for the drivers’ class status. According to California Vehicle Code, cars must yield to a pedestrian if said pedestrian is crossing within any marked crosswalk. Data were collected from an intersection in the San Francisco Bay Area on three weekdays between 2:00 pm and 5:00 pm in June of 2011. A coder, positioned near the crosswalk, rated the approaching car on a scale from 1 to 5 based on make, age, and physical appearance of the car. The lowest status received a code of 1 and the highest status a code of 5. The coder also recorded whether or not the approaching car yielded to the pedestrian (a confederate of the study) waiting to cross. There were 152 drivers who were scored.