Data Analysis:  Graphing Regression Equations

Before proceeding, be sure you understand how to find a regression equation using the calculator.go to regression formulas
Once you have a regression equation from a set of data, it is good to see the graphs.  Starting with the data previously shown in the regression formula demonstration, we can plot both the data and the equation.

  1. Here are the results of the regression procedure.  
    wpe7.jpg (4659 bytes)wpe8.jpg (4543 bytes)







  2. Press the Y= key and set the cursor in the space next to y1= or y2= or any of the other numbered equation lines. 



  3. To enter the regression equation, press the VARS key.varsti83.gif (25862 bytes)












  4. Option 5 is the Statistics option, wpe9.jpg (6899 bytes)
    so press 5
              






    wpeA.jpg (4913 bytes)
  5. Use the right arrow key to highlight EQ
           wpeB.jpg (4951 bytes)  and get








  6. Since choice 1 is highlighted and that is our option, press ENTER
  7. The next screen is the Y= menu again, with the equation entered, in this case, as Y1.wpeD.jpg (5545 bytes)







  8. To see the points as well as the graph, turn on the PLOT feature.  Our datawpeE.jpg (5582 bytes) is in L1 and L2 so we will use Plot1.  Use the UP arrow key to highlight it and press ENTER.  
  9. Press GRAPH     wpeF.jpg (3999 bytes)

How good a fit is it? Not great. Could we do better with a different regression formula?  Here are some other results:

Cubic regression: wpe12.jpg (8884 bytes)    wpe13.jpg (3654 bytes)

Linear regression wpe14.jpg (4954 bytes)   wpe15.jpg (3768 bytes)

 

Both are better than the quadratic, but the cubic is the best of the three.