We’ll show you how to create and interpret the numbers the calculator gives you when you are trying to find a linear regression line or “line of best fit” from a set of data on a TI-84 Plus graphing calculator. This is especially important for statistics students who will have to use this function of their calculator as part of their class. Regression modeling is important in any case where you need to fit a linear function to a set of data, and we’ll walk you through the steps to create a linear regression line on your TI calculator.
StepsPart 1Part 1 of 3:Creating the Formula For the Regression Line1Power on the calculator. Press the ON button at the lower left-hand corner of your calculator.
2Press the STAT button on the calculator. EDIT should appear at the top of your calculator’s screen and “1: Edit” should then be highlighted. Press ENTER at the bottom right-hand corner of the calculator. 
3Input your values. Two columns should appear – one titled L1 and the other titled L2. This will be where you input all of the values from your data set that you should already have ready to go. Put in your X values, or first set of values, under L1. Put your Y or second set of values under L2. After entering a value, press ENTER, and repeat.
4Press 2ND and then MODE buttons to exit the table of values that you’ve created. These values will now be saved in your calculator under the variables L1 and L2, which stand for list 1 and list 2. 
5Press the STAT button again. Press the right arrow until “CALC” is highlighted on the top of your calculator’s screen. Press the down arrow 3 times until “4: LinReg(ax+b)” is highlighted and then press the ENTER button. 
6Make sure that X-list is selected. X-list should already be selected and awaiting a list of data once under “4:LinReg(ax+b)”. This is where you will input your X values, or L1 data values. Press the 2ND button and then the 1 button. This should make L1 appear next to the colons. Press the down arrow once and then Y-list should be highlighted. Press the 2ND button and then the 2 button. This should make the L2 value appear next to those colons. 
7Calculate these values. Press the down arrow until “Calculate” is highlighted at the bottom of the calculator’s screen. Once this is highlighted, press the ENTER button. Part 2Part 2 of 3:Interpreting the Values1Be sure you have properly completed part 1. If you did, you should have 4 variables appear on your screen. These are a, b, r, and r^2 (^ meaning exponent). These variables all have specific meaning to the interpretation of your line.
2Know which values are most important. The values that are most important to the actual line are the a and b values. These can be plugged into the equation y=ax+b as is displayed on the top of your calculator and this will give you the regression line or line of best fit for your data set. The a variable represents the slope of your function. The b variable represents the y-intercept of the graph.
3Understand the other two values. The two other values you are interpreting are r and r^2 are there to help you interpret the fit of your given line to the data set that you provided. The r value tells the strength of the correlation between your X and Y variables. Your r^2 value is the correlation coefficient r squared, which tells you how good of a fit your line is to the data you provided. 
Part 3Part 3 of 3:Troubleshooting (optional)
The following steps only apply if your r and r^2 values don’t show up.
1Press the 2ND button and then press 0. This will take you to a menu with the title “CATALOG”. It should have a long list of commands for your calculator.
2Press the down arrow until the arrow on your screen that points to what command you want your calculator to perform is on “DiagnosticOn”. Press the ENTER button twice.If you now repeat steps 5-7 of part 1, your r and r^2 values should now appear. 
