Unit 6, Lesson 5
Describing Trends in Scatter Plots
Grade 8
Preparation
Lesson Narrative
In this lesson, students are introduced to the terms positive association and negative association. They use fitted lines to help them understand this language and tie it back to their work in an earlier unit on linear relationships. They start to use language to describe trends like, "Cars made in a later year tend to have a higher price." They evaluate the goodness of fit of lines for a given scatter plot (note that this is done informally and in later courses, students will revisit more quantitative measures of fitness) and begin to draw their own lines to fit data in a scatter plot (MP5).
- Draw a linear model to fit data in a scatter plot, and describe (in writing) features of a line that fit data well.
- Draw a linear model to fit data in a scatter plot, and describe (in writing) features of a line that fits data well.
Let’s look for associations between variables.
Required Materials
Activity 2
Required Preparation
Each student needs one strand of pasta. Have extra available in case the strands break.
For the digital version of the activity, acquire devices that can run the applet.
A negative association is a relationship between 2 quantities where one tends to decrease as the other increases. In a scatter plot, the data points tend to group around a line with negative slope.
This scatter plot shows a negative association between the the price of a book and the number of books sold.
A positive association is a relationship between 2 quantities where one tends to increase as the other increases. In a scatter plot, the data points tend to group around a line with positive slope.
This scatterplot shows a positive association between dog height and dog weight.