Scatterplots are used to visualize the relationship or association between two variables. For example, can you say in general that studying more will result in higher grades? We could investigate this by collecting data on how long students studied and perhaps their grade on a final exam and then creating a scatterplot. The overall pattern would help us determine what kind of association time spent studying has with final exam grades.
On the TI83 or 84 series of graphing calculators, getting a scatterplot is pretty easy. Let’s use an example data set to walk through the process.
The table below shows the heights (inches) and weights (pounds) of seven randomly selected players on the Chicago Cubs active roster.
We will use the height as the independent variable (the predictor) and the weight as the dependent variable (the response). Often a textbook will tell you which to treat as x (predictor) and y (response). If not, be sure to check out the article on reading scatterplots to better understand how to choose these variables.
Step 1: Enter the data.
To enter data in your calculator, press [STAT] and then choose 1.Edit.
Now enter the values for x (the predictor) into L1 and the values for y (the response) into L2. Just type the number and press enter to go to the next space.
Press the right arrow to go over to L2. Notice that we keep the data in the SAME ORDER as the original table.
Stept 2: Set up the scatterplot in STAT PLOTS.
To get to the statplot menu, press [2nd] and [Y=] (at the top of the calculator).
Press [ENTER] or 1:Plot 1… to get into the next menu. Once in this menu, highlight [ON] and press [ENTER] to turn the plot on and then make sure that the little graph that looks like a scatterplot is selected for TYPE. You can do this by highlighting it and pressing [ENTER].
Step 3: View the scatterplot
Once plot 1 is on you can press [ZOOM] at the top of the calculator and choose 9:ZoomStat to see the scatterplot.
After pressing [ENTER] or typing 9, the plot should come up!
It doesn’t have any labels or anything, but you can use this to see if perhaps linear regression is appropriate or just to see what kind of pattern is present. Here, it seems that taller players generally weigh more, but since the points are not very close together, the association between height and weight isn’t very strong.
If you want to see which points are which, you can press [TRACE] and use the arrows to jump from point to point.
Problem: When you choose Zoomstat you get an error.
Believe it or not, the most common cause of this is having your calculator in your backpack and having it accidentally type all kinds of stuff in the y-list. I see it every semester! To check, press [Y=] and scroll through to make sure that there is nothing next to any of the y’s on the menu.
Make sure to scroll through the whole list! There can’t be anything there! Also, the only plot highlighted at the top should be PLOT1. The others should not be highlighted.
Problem: Error: DIM
This is a dimension error. It means that the number of values in L1 is different than the number of values in L2. Go back and find which number you left out!
Problem: There is no L1 on your calculator
This is an easy fix. Check out this article for how to get L1 back.