Mean and standard deviation on the TI-80:

Calculating mean and standard deviation on the TI-80:

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. Hit the STAT button and you will see the options EDIT and CALC atop the screen. Use the left and right arrows (if necessary) to move the cursor to EDIT and then hit ENTER.

Now you will see a table with the headings L₁and L₂. Enter the x values under L₁, the y values under L₂. (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, but this time move the cursor to CALC instead of EDIT. 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 2-Var Stats. (If we had only entered a single column of data, 1-Var Stats would be the appropriate choice instead.) Then select L₁ (by hitting 2nd 1), (by hitting the comma key) L₂ (2nd 2). Then hit ENTER.

The calculator will display the x-mean (= 2.5), 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 the sample size (there are n = 4 observations), then the mean and standard deviation of y. (The mean is 5.25, and the standard deviation is s_y =.5).

Now go back to the STAT menu and select CALC, 1-Var stats then L₁ and ENTER. See what happens: we get the mean, sum, and standard deviation of the x's. 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), the median, and finally the sample size.

If you want the median for y, try STAT, CALC, 1-Var stats and then type L₂ before hitting ENTER.

NOTE: The TI-80 does NOT assume that you are using a frequency table.