Mean and standard deviation on the TI-85 and 86

Calculating mean and standard deviation on the TI-85 and 86.
(The instructions below are tailored to the 86, but the 85 is a very similar machine.)

Let's say we have a table of data describing four birds of different species (units of height and weight have been left out here):

height	weight
2	5
3	6
1	5
4	5

You can think of the two columns as representing variables x and y.

First we have to enter the data. Call up the STAT menu (2^nd +) and you will see the options CALC, EDIT, PLOT, DRAW and VARS at the bottom of the screen. Since we want to enter data, select EDIT by hitting F2.

Now you will see a table with the headings xStat, yStat, etc.. Enter the x values under xStat, the y values under yStat. (If you want to clear pre-existing data first, move the cursor to the top of the column, hit CLEAR and then ENTER.)

(If there were only a single variable, we could enter the data as x-values and leave the 2^nd column blank.)

Once all the data is entered, go back to the STAT menu, this time choosing CALC (F1) instead of EDIT (F2). If you can't find your way there, remember: Every TI graphing calculator is equipped with CLEAR, QUIT and/or EXIT commands for getting back out of tough situations.

Once you're in the CALC menu, select TwoVa. (If we had only entered a single column of data, OneVa would be the appropriate choice instead.)

Before hitting ENTER, it is necessary to specify which variables we are interested in. Call up the LIST menu (2^nd -) and then select NAMES (F3) and xStat (F2), yStat (F3). Then hit ENTER.

The calculator will display the x-mean (= 2.5), some other stuff, and then the standard deviation (s_x=1.29). Note that s_x is what we called s in class; the calculator refers to it as s_x so we know that this is the standard deviation of the variable x and not that of y (which will be denoted by s_y). This is followed by something called sigma _x (which is what you would get as standard deviation if you had used n instead of n-1), and finally the sample size (there are n = 4 observations). Use the down arrow to get the corresponding information about y. (Its mean is 5.25, and its standard deviation is s_y = 0.5).

Now go back to the STAT menu and select CALC, 1-Var stats. See what happens: we get the mean and standard deviation of x, and also its five-number summary! If you want the five-number summary for y, try STAT, CALC, 1-Var stats and then yStat (using the LIST menu as above) before hitting ENTER.