Finding Line of Best Fit Using “Q-Points”
Cindy Johnson
1) Have students collect data for a scatter plot and have them enter the data into Ω and æ.
You could also have each student contribute one data point using Navigator, and then send the
entire list back to the kids.
2) Have students find the five number summary for Ω. To do this, push the S key and then
arrow right one place to “CALC.”
You want to choose “1-Var Stats” from the menu and push e. This will show “1-Var Stats”
on your home screen. Enter Ω after this command to get the statistics for your first list. Then
push e. You will need to arrow down to the second half of the screen to find your five
number summary.
Write down the values for Q1 and Q3.
3) Repeat this process in Step 2 for æ and write down Q1 and Q3 for List 2.
4) You are going to use a combination of your quartile points (Q-Points) to help calculate the
line of best fit.
If the data has a positive correlation, your Q-Points are going to be:
(ΩQ1, æQ1) and (ΩQ3, æQ3)
If the data has a negative correlation, your Q-Points are going to be:
(ΩQ1, æQ3) and (ΩQ3, æQ1)
These points give students their (x1, y1) and (x2, y2) for calculating the slope and finding the
equation of the line.
Figure 1
Figure 2
