Standard Deviation on the TI-82/83

Tom Kelliher, MA 114

Sept. 17, 2001

1. Enter independent data into L1 and dependent data into L2.

2. Using the data in L1 and L2, create a least squares model.

3. Compute the residual values for your data. Let's say, for example, your model is (Hiro's model). Recall that the residual is actual y - predicted y. Actual y data is in L2. We can compute predicted y values from the x values in L1 and the linear model. The following calculator equation will compute the residual values and store them in L3:

   L2 - (-4.69 * L1 + 33.12) STO L3
   

   Note carefully that the left-hand side of this line (before the STO) is computing actual y - predicted y.

4. Now, we want to compute the standard deviation of the residual values in L3.

   Press STAT and choose the CALC menu. From the CALC menu choose 1-Var Stats. Your calculator display will now read

   1-Var Stats
   

   We want the 1-Var Stats for L3, the residual values, so press the appropriate keys so that the display reads

   1-Var Stats L3
   

   and press the ENTER key.

   Several values will be computed and displayed. The standard deviation is the value which is preceded by the symbol Sx.