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Algebra 1

3.3.3 Matching Residuals Graphs to Scatter Plots

Algebra 13.3.3 Matching Residuals Graphs to Scatter Plots

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Activity

With a partner, you will take turns to match the graphs of residuals to the scatter plots that display linear models. The scatter plots and their lines of best fit are located on cards A - F. The graphs of the residuals are located on cards G - L.

Matching Activity

1.

Match the scatter plots and given linear models to the graph of the residuals.

2.

Turn over the scatter plots so that only the residuals are visible. Based on the residuals, which line would produce the most accurate estimates? Which line fits its data worst?

What Do Residual Plots Tell Us?

Residuals tell us how close to accurate a line of best fit really is.

Ideally, the residual from a line of best fit will be scattered randomly above and below the horizontal line y=0y=0 on the residual plot. The residual plot would have points above and below the horizontal line y=0y=0. This shows that the relationship between the two variables in the data set can be approximated by a linear model.

When the residuals are equal to 0, this indicates that the line of best fit goes through those points.

A curved pattern shows that a nonlinear model would be better to describe the relationships between points.

Are you ready for more?

Extending Your Thinking

Use the following information to answer questions 1 - 2.

Tyler estimates a line of best fit for some linear data about the mass, in grams, of different numbers of apples. Here is the graph of the residuals.

Scatter plot showing the line of best fit residuals.  The mass (grams) on the y-axis and the number of apples on the x-axis. Data points are scattered at various values from 5 to 11 apples and mass to about 35 grams.
1.

What does Tyler’s line of best fit look like according to the graph of the residuals?

2.

 How well does Tyler’s line of best fit model the data? Be prepared to show your reasoning.

Use the following information to answer questions 3 and 4.

Lin estimates a line of best fit for the same data. The graph shows the residuals.

A scatter plot showing the residuals of the line of best fit.  The mass (grams) on the y-axis and number of apples on the x-axis, with points distributed at various coordinates, some above and some below the x-axis.
3.

What does Lin’s line of best fit look like in comparison to the data?

4.

How well does Lin’s line of best fit model the data? Be prepared to show your reasoning.

Use the following information to answer questions 5 - 6.

Kiran also estimates a line of best fit for the same data. The graph shows the residuals.

A scatterplot showing the residuals of the line of best fit for number of apples on the x-axis (ranging from 5 to 11) and mass in grams on the y-axis (from -20 to 20). Data points are scattered with no clear trend.
5.

What does Kiran’s line of best fit look like in comparison to the data?

6.

How well does Kiran’s line of best fit model the data? Be prepared to show your reasoning.

7.

Who has the best estimate of the line of best fit: Tyler, Lin, or Kiran? Be prepared to show your reasoning.

Self Check

Which residual plot shows the most accurate line of best fit for a scatter plot?

Additional Resources

The Meaning of Residuals

Suppose that you have a scatter plot and that you have drawn the line of best fit on your plot. Remember that the residual for a point in the scatter plot is the vertical distance of that point from the line of best fit. In the previous lesson, you looked at a scatter plot showing how fuel efficiency was related to curb weight for five compact cars. The scatter plot and line of best fit are shown below.

Graph of a scatter plot and line of best fit on a coordinate plane. The x-axis represents the curb weight of a car in hundreds of pounds. The y-axis represents the car's fuel efficiency in miles per gallon. Three of the five data points are labeled. Points A and B lie above the best fit line and point C is located below the line.

Consider the following questions:

  1. What kind of residual does Point A have?
    • Point A has a large positive residual.
  2. What kind of residual does Point B have?
    • Point B has a small positive residual.
  3. What kind of residual does Point C have?
    • Point C has a very large negative residual.
A residual plot that shows curb weight in hundreds of pounds on the x-axis and residual on the y-axis. Four points are above the horizontal axis and one point is below. The residuals for points A, B, and C are labeled.

Try it

Try It: The Meaning of Residuals

Suppose you are given a scatter plot and a line of best fit that looks like this:

Graph of a scatter plot and its line of best fit are drawn on a coordinate plane. As the line slopes upward from left to right, the data points cluster below the line, then they trend above the line, and then the final point lies below the line.

Describe what you think the residual plot would look like.

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