Chapter 8 Regression and Correlation 323
the mortality index can be explained by the change in annual mean tempera-
ture. The remaining 23.46% of the variation is presumed to be due to random
variability.
EXCEL TIPS
You can use the Add Trendline command to add other types
of least-squares curves, including logarithmic, polynomial,
exponential, and power curves. For example, instead of fi tting
a straight line, you can fi t a second-degree curve to your data.
Calculating Regression Statistics
The regression equation in the scatter plot is useful information, but it does
not tell you whether the regression is statistically signifi cant. At this point,
you have two hypotheses to choose from.
H 0 : There is no linear relationship between the mortality index and the
mean annual temperature.
Ha: There is a linear relationship between the mortality index and the
mean annual temperature.
The linear relationship we’re testing is expressed in terms of the regression
equation.
In order to analyze our regression, we need to use the Analysis ToolPak,
an add-in that comes with Excel and provides tools for analyzing regres-
sion. If you do not have the Analysis ToolPak loaded on your system, you
should install it now. Refer to Chapter 1 for information on installing the
Data Analysis ToolPak.
To create a table of regression statistics:
1 Return to the Mortality Data worksheet.
2 Click Data Analysis from the Analysis group on the Data tab to open
the Data Analysis dialog box.
3 Scroll down the list of data analysis tools and click Regression, and
then click the OK button.
4 Enter the cell range C1:C17 in the Input Y Range box.
5 Enter the cell range B1:B17 in the Input X Range box.
6 Because the fi rst cell in these ranges contains a text label, click the
Labels checkbox.
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