The data in the following table come from a time when the United States had a maximum speed limit of 55 miles per hour in all states. An issue of some concern at that time was whether lower speed limits reduce the highway death rate. (These data are called speed limit on the companion website.)
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Highway Death Rates and Speed Limits
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Country
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Death Rate (per 100 million vehicle miles)
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Speed limit (in miles per hour)
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Norway
|
3.0
|
55
|
|
United States
|
3.3
|
55
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Finland
|
3.4
|
55
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Britain
|
3.5
|
70
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Denmark
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4.1
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55
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Canada
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4.3
|
60
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Japan
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4.7
|
55
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Australia
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5.9
|
60
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Netherlands
|
5.1
|
60
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Italy
|
6.1
|
75
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a. In the relationship between death rate and speed limit, which variable is the response variable and which is the explanatory variable?
b. Plot the data in the table, and discuss the result. Does there appear to be an association? Are there any outliers? If so, what is their influence on the correlation?