Technology: Scatterplots on the TI-84

So far we've looked at three basic ways to graph the relationship between two variables: mosaic plots for two categorical variables, side-by-side boxplots for categorical vs. quantitative and scatterplots for two quantitative variables.

The TI-84 cannot create mosaic plots.

To graph side-by-side boxplots, simply put the data for the first group in L1, then set up a boxplot using Plot1 in the StatPlot menu, then put the data for the second group in L2 and set up another boxplot using Plot2, etc. Unfortunately, a maximum of three boxplots are possible on the TI. After you're done, be sure to turn the extra plots Off to avoid errors cropping up when creating graphs in the future.

To create a scatterplot, let's use the size and 2007 assessed value data from the property tax data set we previously investigated as an example:

house	size	assess	lot	taxes	stories
20911	1561	304	0.2	2604	1
20912	1038	297.6	0.2	280	1
20918	1224	289.5	0.17	2353	1
20921	1232	292.8	0.17	756	1
20924	1995	314.6	0.17	2620	2
20927	1714	322.7	0.18	2632	1
20930	1832	336.1	0.18	2779	2
21003	1095	279	0.18	2321	1
21006	2011	319.5	0.18	2663	2
21015	1366	289.3	0.18	2415	1
21018	1292	301.4	0.18	2477	1
21023	1458	314.3	0.18	1386	1
21028	2031	320.9	0.18	2676	2
21105	1366	304	0.18	2473	1

First, enter the data into two lists; here I'll use L1 for size and L2 for assessed value:

enter size data in L1 and assess data in L2

Then go to the STAT PLOT menu, press ENTER to select Plot1, move the cursor to On and press ENTER, move the cursor to the scatterplot icon (the first of the six Type icons) and press ENTER:

turn on Plot1, move cursor to scatterplot icon and press ENTER

Now move to the Xlist line and type L1 and ENTER, then move to the Ylist line and type L2 and ENTER. You can choose whichever Mark you like most.

Next press the ZOOM key, move down to ZoomStat and press ENTER. You should see a scatterplot like this:

scatterplot of size vs. assess

We see a reasonably linear association between size and assessed value, with no noticeable outliers and only a moderate amount of scatter. Notice that there are no scales or labels on this scatterplot. If possible, we should always include these on any scatterplot we use for a HW assignment, project or exam.

You can now press the TRACE button and use the left and right arrow keys to move the flashing cursor from point to point on the scatterplot; as you do, you should see the coordinates of each point listed at the bottom of the screen:

press TRACE and use cursors to navigate from point to point

You might also want to use the WINDOW menu to adjust the scale on each axis.

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