Standard Deviation on TI-84 — 1-Var Stats Guide

The fastest way to get the mean, standard deviation, and five-number summary of a data set on the TI-84 is the built-in 1-Var Stats command. This guide walks through entering data, running the command, reading every line of the output, and — most importantly — knowing whether to report Sx or σx.

Step 1: Enter your data into a list

1. Press STAT, then choose 1: Edit
2. Type each value into L1, pressing ENTER after each one
3. To clear old data first: arrow up to highlight the L1 header itself, press CLEAR, then ENTER

Warning: never press DEL while the L1 header is highlighted — that removes the entire list from the editor instead of clearing it. CLEAR then ENTER is the safe way.

Step 2: Run 1-Var Stats

1. Press STAT, then arrow right to the CALC menu
2. Choose 1: 1-Var Stats
3. At the List: prompt, enter L1 by pressing 2nd 1
4. Leave FreqList: blank (only used for frequency tables — see below)
5. Highlight Calculate and press ENTER

Step 3: Read the output

Run it on this sample data set — five quiz scores: 5, 7, 8, 9, 6.

Keystrokes:

STAT → 1: Edit → enter 5, 7, 8, 9, 6 into L1
STAT → CALC → 1: 1-Var Stats → List: L1 → Calculate

Screen output:

1-Var Stats
 x̄ = 7
 Σx = 35
 Σx² = 255
 Sx = 1.58113883
 σx = 1.414213562
 n = 5
 minX = 5
 Q1 = 5.5
 Med = 7
 Q3 = 8.5
 maxX = 9

Sx vs σx — which one do you report?

This is the question that costs students points. The calculator shows both, and they are never equal.

On AP Statistics, the answer is almost always Sx. Exam data nearly always comes from a sample (a survey, an experiment, a random selection), so report Sx unless the problem explicitly says you have the whole population. In the example above you would write: "The sample standard deviation is Sx ≈ 1.581."

A quick sanity check: Sx is always slightly larger than σx, and the gap shrinks as n grows.

Frequency table example (using FreqList)

When data comes pre-summarized in a frequency table, don't type repeated values — put the values in L1 and the frequencies in L2.

Question: Ten students scored as follows: 80 (3 students), 85 (5 students), 90 (2 students). Find the mean and sample standard deviation.

1. Press STAT 1: Edit
2. Enter 80, 85, 90 into L1
3. Enter 3, 5, 2 into L2
4. Press STAT → CALC → 1: 1-Var Stats
5. List: L1 (2nd 1), FreqList: L2 (2nd 2), then Calculate

Screen output (key lines):

1-Var Stats
 x̄ = 84.5
 Sx = 3.689323937
 σx = 3.5
 n = 10

The calculator correctly treats this as 10 data points, not 3. If n on your output screen doesn't match the total frequency, you forgot the FreqList entry.

Common mistakes

• Reporting σx on a sample problem. The grader expects Sx ≈ 3.689 here, not 3.5.
• Leftover data in L1. Old values mixed with new ones silently corrupt every statistic. Always clear the list first.
• Forgetting FreqList with a frequency table. Running 1-Var Stats on L1 = alone gives x̄ = 85 and n = 3 — wrong data set entirely.
• Confusing standard deviation with variance. The TI-84 reports standard deviation. If a problem asks for variance, square it: Sx² = 1.5811² = 2.5.

Where to go next

Once your data is in L1 and L2, the same STAT → CALC menu does much more — see the linear regression guide for fitting a line with LinReg, and the confidence intervals guide for turning Sx and x̄ into a t-interval. If you only need quick one-variable stats on a scientific calculator, the online TI-30XS has a similar data/stat feature.

Practice right now

Open the free online TI-84 calculator — a full TI-84 Plus CE in your browser, no download or account needed — and run both examples above. Enter 5, 7, 8, 9, 6 into L1, run 1-Var Stats, and confirm you get x̄ = 7 and Sx ≈ 1.581. Then try the frequency-table version and check that n = 10. Doing it once yourself locks in the workflow before test day.