Residuals on the TI-85
by Tom Linton, http://www.central.edu/homepages/lintont
Here is one way to calculate (rather quickly, once you're used to it) residuals from a linear regression on the TI-85.
  1. Using the statistical editor, enter the X values of the data in the list named xStat and the Y values of your data in the list named yStat.
  2. Open the [STAT] [CALC] menu (press [STAT][F1] and accept xStat and yStat as the lists, by pressing [ENTER] twice) and press [F2] to run a linear regression. The intercept a, and the slope b, should appear on your screen. The least squares regression equation is y = a + b*x. Press [MORE] and then [F4] to store the regression equation. The phrase "NAME =" should appear. Press [2nd][ALPHA] [y] [ALPHA][ALPHA] [1] to give the variable name y1 and then press [ENTER]. This step should store the regression equation as y1. Press [GRAPH][F1] to ensure that the equation was properly stored as y1.
  3. Press [2nd][QUIT] to return to the home screen. Store the X data values in the variable x by giving the command
xStat [STO>] [x-VAR].
    That is, press [2nd][LIST][F3] to view the names of your lists. Press the appropriate function key or [MORE] to select the name xStat. This will paste the word "xStat" on your home screen. Next, press the store button (near the lower left of the keypad), then the [x-VAR] button and finally press [ENTER]. The first few values of your X data will be displayed.
  1. Store the values of the residuals in the user defined list named RES by executing the command
yStat - y1 [STO>] RES
You can find the list yStat under [2nd][LIST][F3] (list names), or simply type it in, but use a lowercase "y", uppercase "S" and lowercase "tat". You get uppercase letters from the [ALPHA] key and lowercase letters by pressing [2nd][ALPHA]. Next, enter the subtraction key (the black one, not the grey one), press [2nd][ALPHA][y][1] to "type out" the name y1, press [STO>] (the store key near the lower left of the keypad) and then type [R][E][S] and [ENTER]. This command tells the calculator to make a list of values of the form "true y value" (yStat) minus "predicted y value" (y1). It is mandatory that the X data points are stored in "x" before issuing this command.
The residuals are now in the list named RES. If you enter RES and press [ENTER] from the home screen, the values will be displayed and you can use the left and right arrow keys to scroll through them. You can also use the statistical editor to view them by selecting xStat as the X data list and RES as the Y data list.