1. Scatter Plots Learning Goals
Students will be able to construct a scatter plot.
Students will be able to describe the relationship between the two quantitative variables.
Students will be able to predict values using a trend line (or line of fit)
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2. Let’s define Scatter Plot.
A scatter plot is a graph of bivariate data in the coordinate plane.
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3. Advantages of using a scatter plot:
Represents a visual display of a large amount of data.
Makes it easy to see a relationship between two variables, if one exists.
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4. The correlation coefficient is a measure of the strength of a linear relationship between two variables. It can be:
Positive,
Negative, or
Zero
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5. How are the variables related?
Number of text messages sent. (y) 40 55 31 52 38 45 60 74 54
Days (x) 1 2 3 4 5 6 7 8 9
Number of Texts
Day
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6. Analyze the graph; then think/write/pair/share (3 minutes).
Questions to consider:
What two variables are related in the scatterplot?
Is there any evidence of a linear relationship?
If so, how would you describe the relationship?
How would you describe the strength of the relationship?
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7. Making predictions using a trend line:
Locate the value of an independent
variable on the trend line and then identify
the value of its dependent variable.
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8. Point (0,10) and (8,80) used for slope and 10 is y intercept
Let’s practice:
Are the variables correlated? If so, is it positive or negative?
Draw a trend line or line of fit.
Use the graph to estimate how many text messages will be sent on day 10.
Next, write the equation of the line of fit. Use slope-intercept form, y = mx + b.
Now, use the equation to predict the number of texts sent on the tenth day. Compare this prediction to your previous estimate.
(Yes - positive)
(About 100)
y= 8.75x +10
Point (0,10) and (8,80) used for slope and 10 is y intercept
y = 8.75(10) +10
y =
y = 97.5 texts
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9. Guided Practice: Create data for the variables shown on the graph and then graph the data.
Daily Use of Cell Phones and Homework
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10. Is there a correlation between the
number of hours spent using a cell phone and the number of hours
spent doing homework?
Draw a trend line or line of fit.
Predict the number of hours of cellphone use for a person who studies for 0.5 hours.
Next, write the equation of your line of fit in slope-intercept form.
Now use the equation to predict the number of hours of cellphone use for a person who studies for 0.5 hours.
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