Lesson 19

Fitting a Line to Data

Lesson Narrative

In the previous lesson, students focused primarily on the details of a scatter plot. In this lesson, their focus becomes more holistic and they begin to see a set of data points as a single thing that can be analyzed, not just a bunch of disconnected points. For the first time students see that sometimes we can model the relationship between two variables with a line (MP4), although they continue to analyze the connections between the scatter plot and the line by comparing individual points. As they zoom out and see these connections, students begin to see the structure of the scatter plot (MP7) and to use that structure to reason abstractly and quantitatively (MP2).

Teacher Notes for IM 6–8 Math Accelerated
Students may bring up the use of the word “function” in this lesson and several of the following lessons. Due to the sequence of IM 6–8 Math Accelerated, this lesson now comes before the unit where functions and function language is introduced. For now, tell students they can think of “function” as another way to talk about a relationship between inputs and outputs and that they will learn more about functions in a future unit. In this unit, the focus is on inputs and outputs that have a linear relationship.

Learning Goals

Teacher Facing

• Compare and contrast (orally) values in a data set with predictions made using a given line.
• Comprehend that a model of data, such as a line of fit, can be used to predict values that are not given in the data.
• Identify (orally) obvious outliers on a scatter plot.

Student Facing

Let’s look at the scatter plots as a whole.

Student Facing

• I can pick out outliers on a scatter plot.
• I can use a model to predict values for data.

Glossary Entries

• outlier

An outlier is a data value that is far from the other values in the data set.

Here is a scatter plot that shows lengths and widths of 20 different left feet. The foot whose length is 24.5 cm and width is 7.8 cm is an outlier.