Transcript ex27

Example 2.7
Analyzing Relationships with Scatterplots
ACTORS.XLS

Recall that this data set contains information on 66
movie stars including their, Gender, Domestic Gross,
Foreign Gross and Salary.
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We might guess that stars whose movies gross large
amounts have the largest salaries. Is this true?
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Scatterplots
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We are often interested in the relationship between
two variables.
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A useful way to picture this relationship is to plot a
point for each observation, where the coordinates of
the point represent the values of the two variables.
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The resulting graph is a scatterplot.
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Scatterplots -- continued
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After constructing a scatterplot, we can examine the
scatter of points.
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We can usually see whether there is any relationship
between the two variables, and, if so, what type of
relationship it is.

We will use a scatterplot to determine if the statement
about the relationship between movie gross and
salaries is true.
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Creating a Scatterplot
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To analyze this we need to plot each star’s salary on
the vertical axis and the corresponding domestic
gross on the horizontal axis.
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To create this scatterplot:
– Place the cursor anywhere in the data set.
– Select the StatPro/Charts/Scatterplot menu item.
– Select Salary as the Y variable, Domestic Gross as the X
variable and give the chart sheet a name such as Scatter.
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The Resulting Scatterplot
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Analyzing the Scatterplot
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The message is clear. The points tend to move up
and to the right. This means that stars in films with
large domestic grosses tend to make the largest
salaries.
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The correlation of 0.61 shown in the chart supports
this conclusion. As we will see in Chapter 3, this
implies a reasonably strong positive linear
relationship between the two variables.
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