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Solving Linear Regression Problems Using the TI 83 Graphing Calculator
An AskERIC Lesson Plan

Supose you have some data:

The goal of this tutorial is to help you...

...make a scatterplot of the table above on your graphing calculator.

...graph the Linear Regression Equation in the form y = mx + b

Do the following...

1. Let's begin solving the asteroid problem given above by entering our data points into 2 lists in the calculator. The lists are found under the STAT key.
2. To enter or edit data points, which is what we want to do, you must use the EDIT menu.
3. Tap STAT, then the EDIT menu, then edit again. Enter the values for the asteroids' distances into the first list, which the calculator creatively calls L1. Enter the asteroids' orbital periods into the second list, L2.
4. To plot these data points on a graph, we must create a stat plot; this key is located above the Y= key, just below the screen on the far left. Hit the STAT PLOT key.
5. Now, you must choose Plot 1 by turning it dark, or selecting it, by moving the cursor on top of it (use the arrow keys). Now, hit ENTER; now that you're inside the Plot 1 area, turn it on by selecting ON, then hit ENTER.
6. Select the first graph to draw, let the Xlist be L1 and let the Ylist be L2. The bottom line inside here lets you choose what kind of marks you want on your graph: dots, little plus signs, or little squares. Select whichever one you like best. We are now ready to graph!
7. In order to see your points on the graph, we must set the window up accordingly. Hit the WINDOW key. Our lowest X value (smallest distance) in L1 is 204.4 , so let's let Xmin = 200. Our largest X value is 257.4 , so let Xmax = 260. Since the difference between Xmax and Xmin is 60 , let the Xscl = 10. That way, our x-axis will show 6 marks each 10 units apart. Similarly, let Ymin = 3, Ymax = 6, and Yscl = 1.
8. Now graph the scatterplot by hitting GRAPH.
   If you don't see your scatterplot, here are a couple of possible reasons why:
   1. If your calculator says, ERR: DIM Mismatch, check your 2 lists to see if you have the same number of elements in each list (you may not). Do this using STAT , EDIT, edit.
   2. If nothing appears on your graph, you may not have turned Plot 1 on. Do STAT PLOT, then turn Plot 1 on. Now, hit GRAPH again.
   3. Your Window is not set up as you thought it was. Hit WINDOW and check it.
9. It's time to get the linear regression line to go through the scatterplot. Hit STAT, go to the CALC menu, then choice #4, LinReg(ax + b). This will take you to the home screen, showing you LinReg (ax+b). Hit ENTER, and values for a and b will be given.
10. You should get:

You can write these values down and then go into the Y= menu, then manually type in
y = .0196x - .3963

OR, you can import these values, letting the calculator copy them in for you. To do this, hit the y= key. (Clear out any equations currently in here.) Put the cursor to the right of \Y1 = . Let's find the linear regression equation and put it here.

Hit the VARS key located just below the down arrow key. Go to #5, statistics, and enter this. See the new menu at the top? The regression equation is under the EQ menu, so select EQ using the right arrow key. Now, choice #1 is RegEQ... select this one, then hit ENTER. Your regression equation should have been copied into the Y1 = section of the calculator, and it should be in the form y = ax + b. Now, hit GRAPH, and you should see the line of regression cut through the scatterplot.