Directions for Performing Linear Regression

Before you begin, clear out all old data. Go to Y= and delete any equation you have entered.

1. Create a scatter plot by entering data. Use the data below:

Year 1997 1998 1999 2000 2001 2002Sales 27.9 28.7 30.2 32.5 33.1 34.3

Press STAT and select Edit. Enter the years since 1997 (0,1,2,3,4,5) into List 1 (L1). These will be X values.

Enter sales (in billions of dollars) into List 2 (L2). These will be y values.

2. Choose plot settings. Press 2nd Y= and select Plot 1. Turn Plot 1 On. Select Scatter Plot for the type of display. Enter L1 for the X List and L2 for the Y List.

3. Make a scatter plot. Press ZOOM 9 to display the scatter plot so that the points for all data pairs are visible.

4. Describe the correlation. Is it positive or negative?

5. Find the equation for the best fitting line.

6. First perform regression. Press STAT. From the CALC menu, choose LinReg (ax + b) [it’s number 4]. The a and b values are from the equation y = ax + b. The calculator will find the slope and intercept for the best fitting line based on the data you entered. It will also calculate the r value.

7. R value: is the correlation coefficient. It measures how well the best fitting line fits the data. For an r close to 1, there is strong positive correlation. For an r close to -1, there is strong negative correlation. For r close to zero, the data has relatively no correlation. In this example, the r is .98817, which is close to 1. There is strong positive correlation.

8. Draw the best fitting line. Press Y= and enter the equation for the line. In this case, 1.36 X + 27.7 for Y1. Press GRAPH.

9. If you press TRACE and the up arrow, you can trace the line you’ve created and see the X and Y values for each point on the line.