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Scatter Plots
A scatter plot is a graph with points plotted to show a relationship between two sets of data.
Correlation describes the type of relationship between two data sets.
The line of best fit is the line that comes closest to all the points on a scatter plot. One way to estimate the line of best fit is to lay a ruler’s edge over the graph and adjust it until it looks closest to all the points.
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Scatter Plots
Positive correlation: both data sets increase together.
Negative correlation: as one data set increases, the other decreases.
No correlation: changes in one data set do not affect the other data set.
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Non-Linear:No straight line of best fit can be formed through the points.
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The size of a jar of baby food and the number of jars of baby food a baby will eat.
Negative correlation: The more food in each jar, the fewer number of jars of baby food a baby will eat.
Do the data sets have a positive, a negative, or no correlation?
Scatter PlotsUnit 6
Do the data sets have a positive, a negative, or no correlation?
The speed of a runner and the number of races she wins.
Positive correlation: The faster the runner, the more races she will win.
Scatter PlotsUnit 6
Do the data sets have a positive, a negative, or no correlation?
The size of a person and the number of fingers he has.
No correlation: The size of a person will not affect the number of fingers a person has.
Scatter Plots
Use the given data to make a scatter plot of the weight (y) and height (x)of each member of a basketball team, and describe the correlation.
Example 1: Making a Scatter Plot of a Data Set
The points on the scatter plot are (71, 170), (68, 160), (70, 175), (73, 180), and (74, 190).There is a positive correlation between the two data sets.
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Scatter Plots
Use the given data to make a scatter plot of the weight and height of each member of a soccer team, and describe the correlation.
Example 2:
12062
13568
17569
15667
12563
Weight (lbs)Height (in)200
190
180
170
160
150
140
130
120
60 61 62 63 64 65 66 67 68 69
The points on the scatter plot are (63, 125), (67, 156), (69, 175), (68, 135), and (62, 120). Height
Weig
ht
There is a positive correlation between the two data sets.
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Scatter Plots
Line of Best Fit…A line that comes close to all
the points on a scatter plot.
Hint: Try to draw the line so that about the same number of points are above the line as below the line.
Scatter Plots
Make a scatter plot of the data, and draw a line of best fit. Then use the data to predict how much a worker will earn in tips in 10 hours.
Example 3: Using a Scatter plot to Make Predictions
Tips earned may be dependent on the number of hours worked.
Step 1: Make a scatter plot.
Let hours worked represent the independent variable x and tips earned represent the dependent variable y.
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Scatter PlotsAdditional Example 2 Continued
Step 2: Draw a line of best fit.
Draw a line that has about the same number of points above and below it.
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Scatter PlotsAdditional Example 2 Continued
Step 3: Make a prediction.
According to the graph, working 10 hours will earn about $24 in tips.
Find the point on the line whose x-value is 10. The corresponding y-value is about 24.
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Scatter Plots
Formative Assessment:Are you really getting scatter plots and lines of best fit??
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Scatter Plots
1. Use the given information to make a scatter plot, and describe the correlation.
Grading Period 1 2 3 4
Number of A’s 5 6 8 10
positive correlation
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Scatter Plots
2. Draw a line of best fit for the scatter plot you drew in Problem 1. Then use the data to predict the number of A’s in grading period 6.
approximately 13 A’s
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Scatter Plots1. Identify a scatter plot for the given data.
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A.
B.
Scatter Plots
2. Do the data sets have a positive, a negative, or no correlation?distance covered and time taken at constant speed
A. positive
B. negative
C. none
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Scatter Plots
3. Do the data sets have a positive, a negative, or no correlation?value of a used car and the total distance traveled
A. positive
B. negative
C. none
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