# TI-83 Instructions

## Computing a Sample Variance and Standard Deviation

### Method 1 (Special keys)

1. Press `STAT`.
2. Select the `CALC` menu title.
3. Select item #1, `1-Var Stats`.
4. Press `ENTER`. The phrase `1-Var Stats` appears in the display.
5. Press `2nd L1`.
6. Press `ENTER`. A list of statistics appears. The fourth one in the list, `Sx`, is the sample standard deviation. (Be careful not to use `σx`. It represents the population standard deviation.)

### Method 2 (Alternative Formula)

1. Enter the expression `sum(L1^2) - sum(L1)^2`.
2. Press `÷` (divide).
3. Enter the sample size.
4. Press `ENTER`.
5. The display now shows the sum of the squared deviations, i.e., SS(x). From here on, follow steps 11 - 17 under Method 3 below.

### Method 3 (Standard Formula)

1. Compute the mean of `L1`. (See Computing a Mean.)
2. Press `L1`.
3. Press `-` (minus).
4. Enter the mean.
5. Press `ENTER`. The display shows a list of deviations.
6. Press `STO`.
7. Press `2nd L2`.
8. Press `ENTER`. The deviations are now stored in list `L2`.
9. Enter the expression `sum(L2^2)`.
10. Press `ENTER`. The display now shows the sum of the squared deviations, i.e., SS(x).
11. Press `÷` (divide).
12. Enter one less than the sample size, i.e., n` - 1`.
13. Press `ENTER`. This gives the variance.
14. Press the square root key. The square root symbol appears.
15. Press `2nd ANS`. The expression `Ans` appears after the square root. This refers to the result of the previous calculation, which in this case is the variance.
16. Press `)`.
17. Press `ENTER`. The display now shows the standard deviation.