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# When you determine if there is an association between two variables, it is also important to determine how strong or weak that association is.

When you determine if there is an association between two variables, it is also important to determine how strong or weak that association is. This is why, when you have data for two quantitative variables, you calculate what is called the coefficient for correlation. Solve problems involving the coefficient for correlation.

Instructions

1. Suppose you are determining the association between the weight of a car and the miles per gallon that the car gets. Answer the following questions in a Word document:
• Define correlation and talk about how you can use correlation to determine the relationship between these two variables.
• Before you look at some data, what kind of association do you think will exist between the weight of a car and the miles per gallon that the car gets? Will it be positive or negative?
• Given the data below, use Excel or other technology to calculate the correlation coefficient for this data:

Model

City MPG

Weight

Mazda MX-5 Miata

25

2365

Mercedes/Benz SLK

22

3020

Mitsubishi Eclipse

23

3235

Pontiac Firebird

18

3545

Porsche Boxster

19

2905

Saturn SC

27

2420

• Now that you have calculated the correlation, what does this value represent? What does it tell you about the relationship between these two variables?

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