Chapter 3.2, Problem 80E

(a)

To determine

To make a graph that displays the accident rate for each category of marijuana use. And explain is there evidence of an association between marijuana use and traffic accidents.

Answer to Problem 80E

Yes, there is evidence.

Explanation of Solution

Now, the ratio of the accidents in each groups will be as:

Never: $\frac{59}{452}=0.1305$

  $\begin{array}{l}\text{1-10 times: }\frac{36}{229}=0.1572\\ \text{11-50 times: }\frac{15}{70}=0.2143\\ \text{51+ times: }\frac{50}{156}=0.3205\end{array}$

Thus the histogram of the data will be as:

  

Since the height of the bars increase as the marijuana use per year increases, there is evidence of an association between marijuana use and traffic accidents.

(b)

To determine

To explain why we cannot conclude the marijuana use causes accidents based on this study.

Explanation of Solution

As we can say that we can't prove causation, because we don't know if the subjects drive under influence of marijuana when they cause an accident and people also might be untruthful about their marijuana use. Moreover there might be lurking variables such as overall drug use and interest in safe driving that affect the results of the study. A lurking variable is a variable that has an important effect on the relationship among the variables in a study but is not one of the explanatory variables studied.