Linear Regression on TI-84 — LinReg Step by Step

Enter your data, run LinReg, and get the equation ŷ = a + bx — plus r and r² — in under two minutes.

Before You Start: Turn DiagnosticOn

By default, the TI-84 hides r and r² after running LinReg. You need to enable diagnostics once, and it stays on permanently.

1. Press 2ND → 0 to open the CATALOG
2. Press D to jump to entries starting with D
3. Scroll down to DiagnosticOn
4. Press ENTER twice

You'll see Done on the screen. Now r and r² will always appear in your LinReg output.

This is the single most common reason students can't find r on their TI-84. Do this step first.

Step 1: Enter Your Data into Lists

1. Press STAT → 1: Edit
2. Enter your x-values in L1 (press ENTER after each)
3. Move to L2 and enter your y-values in the same order
4. Press 2ND → MODE to quit when done

Example data (hours studied vs. exam score):

Step 2: Run LinReg

1. Press STAT
2. Arrow right to CALC
3. Select 4: LinReg(ax+b)
4. The command appears on the home screen: LinReg(ax+b)
5. Press ENTER

Reading the LinReg Output

y = ax + b
a = 6.4
b = 51.2
r² = 0.994
r = 0.997

Your regression equation: ŷ = 6.4x + 51.2

Writing the AP Statistics Regression Sentence

For the slope (most commonly tested):

"For each additional [x-unit], the predicted [y-variable] increases/decreases by [|a|] [y-units]."

For r²:

"Approximately [r² × 100]% of the variation in [y-variable] is explained by the linear relationship with [x-variable]."

For our example:

"For each additional hour studied, the predicted exam score increases by 6.4 points." "Approximately 99.4% of the variation in exam scores is explained by the linear relationship with hours studied."

Step 3: Draw the Scatter Plot and Regression Line

Set up the scatter plot:

1. Press 2ND → Y= to open STAT PLOTS
2. Select Plot1 → press ENTER
3. Set On, Type: scatter (first icon), Xlist: L1, Ylist: L2
4. Press ZOOM → 9: ZoomStat — this auto-fits the window to your data

Add the regression line:

1. Press Y=
2. In Y1, press VARS → 5: Statistics → arrow right to EQ → 1: RegEQ
3. Press GRAPH

The regression line now appears over your scatter plot.

Making Predictions with the Equation

To predict y for a given x value:

Method 1 — Use the equation directly: ŷ = 6.4(4.5) + 51.2 = 28.8 + 51.2 = 80

Method 2 — Use the graph:

1. Press TRACE
2. Arrow right/left to move along the regression line
3. The x and y values appear at the bottom of the screen

Extrapolation warning: Only predict within the range of your x data. Predicting outside this range (extrapolation) is unreliable — mention this on AP free response.

Common Mistakes

1. r and r² not showing up You haven't run DiagnosticOn. See the first step above — it only needs to be done once.

2. Using LinReg(a+bx) instead of LinReg(ax+b) Both calculate the same line, but the letters are swapped. LinReg(ax+b) uses a for slope and b for intercept — the AP Statistics convention. Be consistent with whichever you use.

3. Confusing r and r² r = correlation coefficient (ranges from −1 to 1, measures direction and strength). r² = coefficient of determination (ranges from 0 to 1, interpreted as a percentage of variation explained). They are different numbers — don't swap them in your conclusion.

4. Forgetting context in the conclusion "The slope is 6.4" gets partial credit. "For each additional hour studied, the predicted score increases by 6.4 points" gets full credit. Always include context.

Practice running LinReg on the free TI-84 calculator with your own data.

Open TI-84 Calculator →

Related Guides

• Hypothesis Testing on TI-84 — Z-Test, T-Test & Proportion Test
• Confidence Intervals on TI-84 — ZInterval, TInterval & More
• IB Math TI-84 Reference Guide