How to Calculate Correlation on the Ti-84 Plus
The correlation coefficient, also known as the "r^2" value, is extremely important in statistics. It allows statisticians to calculate how closely data follows the trend shown by the line of best fit. Often, it is also used to show the variability of a data set. It is easy to find the correlation coefficient of a set of data using a TI-83 or TI-84 graphing calculator.
Press "Stat" and hit "Enter." Several empty tables will appear, labeled "L1," "L2," and "L3."
Type your x-values into "L1." Be sure to press "Enter" after every value to move the cursor to the next row.
Use the right arrow key to move the cursor to "L2" and type in your y-values.
Press "2nd" (the yellow button on the left) followed by "Y=" (the first blue button at the top). Press "Enter" and a screen with many graph choices will appear.
Use the arrow keys to move. Highlight "On" and press "Enter." Move down and highlight the first picture, which shows a scatterplot. Press "Enter." Make sure that "Xlist" reads "L1" and "Ylist" reads "L2." If they do not, move the cursor to "Xlist" and press "2nd" followed by "1." Then move the cursor to "Ylist" and press "2nd" followed by "2."
Press "Graph" (the last blue button at the top) and be sure your graph looks right. If a point or several look incorrect, return to "Stat," "1" and be sure your values are entered correctly. While viewing your graph, decide if it looks linear, quadratic, cubic or quartic.
Press "Stat" and the right arrow key. Scroll down to highlight "LinReg," "QuadReg," "CubicReg", or "QuartReg" based on what you decided in the previous step. Press "Enter" twice. After some thinking, your calculator will display an equation with values, an "r^2" value, and an "r" value. The "r^2" value is the coefficient of determination and describes the correlation of your graph.
Tips & Warnings
- If you get the error "Dim Mismatch" when you try to graph, check your tables. This error means that you have a different number of x- and y-values, so the points don't match up.