Let's say we have a table of data describing four individual birds (units of height and weight have been left out here):
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The first thing we have to do is enter the data in the calculator. Go to the STAT menu (by typing 2nd, MATRX). The options 'CALC', 'DRAW' and 'DATA' appear across the top of the screen. Select 'DATA' (by moving to that word using the left-right arrows and then hitting ENTER). Then select 'Edit'. (ClrStat is another option on this screen, which will clear any data that's already on there.)
You will see
x1=
y1=1
In class we wrote these as "x1", "y1", etc., but your calculator can't write subscripts so x1 appears as "x1".
Since we have two columns worth of data, we can enter them here as
x1=2 y1=5
x2=3 y2=6
etc.
(If there were only a single variable, we would enter it as x-values and leave the y-values blank (although the TI-81 puts 1's in for each y, just as place-keepers).
If there is already data in the table from a previous problem and you need to clear it, go back to the DATA screen and select ClrStat before entering new data.
Once all the data is entered, go back to the STAT menu, but this time select 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 one-var statistics.
The words one-var will then appear on the screen. If you simply hit ENTER,
The calculator will display the sample size (there are four observations), the mean (2.5), and the standard deviation (1.25) for the variable x.
If instead we followed the words one-var with Y before hitting ENTER, we would have gotten the corresponding information for the variable y.