Model Notes

 

****Remember the model we create is only as good as the data we have available!!!

 

What is a model?

          A model is a function that predicts what can/did happen based on prevailing trends in the available data.

 

How do we set up a model in the calculator?

          The first year of available data is called the baseline year, and we assign that year the value 0. Every year after that has a t-value calculated from the baseline. Look at the first model from your book on p. 44. (I have calculated the t-values for you.)

 

Year

t

CO2C(t)

1965

0

319.9

1970

5

325.5

1980

15

338.5

1990

20

354.0

1995

30

360.7

 

Set up the data points in L1 and L2 as prescribed in the calculator notes. Recall that the values in the concentration column are called actual values because they come from the original measured data available for CO2 concentration levels in the atmosphere. After getting the regression equation on the above data from your calculator, we have the function CO2C(t) = 1.38t + 319.02. Type this equation into Y1 in your calculator, replacing x for t in the equation. Follow the prescribed steps to get the graph—scatter plot and line on your calculator.

 

          Now you are ready to get the predicted values from the model function.

1.  STAT   Edit   ENTER and highlight L3 above the third column. ENTER. (You should have the cursor at the bottom of this screen waiting for

the equation for this column.)

2.  Type in the following equation:  1.38L1 + 319.02 and press ENTER. L3 should now give you the list of predicted values from the model

function. Remember L1 stores the t-values for our calculations of concentration levels.

 

3.  The next column, L4, calculates the error of each data item. Highlight  L4 and press ENTER. Then go to MATH   Num   abs   ENTER.

4.  Type in L2 – L3) so it looks like this:  abs(L2 – L3) and ENTER. The values that appear in the L4 column are the positive differences of the actual

and predicted values.

5.  The last thing we need is the TOTAL ERROR. On the calculator do 2ND  QUIT,  2ND  LIST  Math   5.  Type in L4) ENTER so it looks like this:

sum (L4) and the calculator reports the TOTAL ERROR from that column, L4.