The previous exercise gave data on seat belt use for each of the 50 U.S. states and the District of Columbia (“Traffic Safety Facts,” National Highway Traffic Safety Administration, June 2015). The observations represent the percentage of drivers wearing seat belts in a large nationwide observational survey. 

Some, but not all, states enforce seat belts laws. Below are the seat belt usage data divided into two groups—states that enforce seat belts laws and those that do not. 

States with Seat Belt Law Enforcement: 

95.7 88.4 74.4 97.1 85.1 91.9 93.2 88.8 97.3 93.5 94.1 90.2 92.8 85.7 86.1 84.1 85.0 92.1 93.3 94.7 78.3 87.6 92.1 90.6 90.6 86.3 97.8 87.4 90.0 68.9 87.7 90.7 94.5 87.8 84.7 

States without Seat Belt Law Enforcement: 

87.2 82.4 80.2 76.6 78.8 74.0 70.0 94.0 70.4 81.0 85.0 83.6 68.9 83.4 84.1 77.3 79.2 

a. Construct a comparative stem-and-leaf display using the tens digit as the stem and truncating the leaves to a single digit (the ones digit). 

b. Write a few sentences commenting on similarities or differences in the seat belt use distributions for states with seat belt enforcement and states without seat belt enforcement.