CHAPTER 16 Getting Straight Talk on Straight-Line Regression 217

Fortunately, most statistical packages can perform a straight-line regression.

Microsoft Excel has built-in functions for calculating the slope and intercept of

the least-squares straight line. You can also find straight-line regression web

pages (several are listed at https://statpages.info). If you use R, you can

explore using the lm() command. (See Chapter 4 for an introduction to statistical

software.) In the following sections, we list the basic steps for running a straight-

line regression, complete with an example.

Taking a few basic steps

The exact steps you take to run a straight-line regression depend on what soft-

ware you’re using, but here’s the general approach:

1.

Structure your data into the proper form.

Usually, the data consist of two columns of numbers, one representing the

independent variable and the other representing the dependent variable.

2.

Tell the software which variable is the independent variable and which

one is the dependent variable.

Depending on the software, you may type in the variable names, or pick them

from a menu or list in your file.

3.

If the software offers output options, tell it that you want it to output

these results:

• ^{Graphs of observed and calculated values}

• ^{Summaries and graphs of the residuals}

• ^{Regression table}

• ^{Goodness-of-fit measures}

4.

Execute the regression in the software (tell it to run the regression).

Then go look for the output. You should see the output you requested in

Step 3.

Walking through an example

To see how to run a straight-line regression and interpret the output, we use the

following example throughout the rest of this chapter.

Consider how blood pressure (BP) is related to body weight. It may be reasonable

to suspect that people who weigh more have higher BP. If you test this hypothesis