Activity
Each of the scatter plots shows a strong relationship. Write a sentence or two describing how you think the variables are related.
1. During the month of April, Elena keeps track of the number of inches of rain, or precipitation, recorded for the day and the percentage of people who come to school with rain jackets.
Compare your answer:
Your answer may vary, but here is a sample.
When there is more rain, it is more likely people will wear jackets.
2. A school book club has a list of 100 books for its members to read. They keep track of the number of pages in the books the members read from the list and the amount of time it took to read the book.
Compare your answer:
Your answer may vary, but here is a sample.
Longer books will take more time to read.
3. Number of tickets left for holiday parties at a venue and noise level at the party
Compare your answer:
Your answer may vary, but here is a sample.
When more tickets are left, the party will have fewer people to have loud conversations, so it will be quieter.
4. The height and score on a test of vocabulary for several children ages 6 to 13
Compare your answer:
Your answer may vary, but here is a sample.
Children who are taller are usually older, so they have had more time to be in school and learn more vocabulary.
Why Should I Care?
One of the most powerful tools you can give a farmer to help improve their crop is statistics. Statistics can help farmers at every stage. For example, seeds are expensive, and if you plant too many strawberries in a market where there are hundreds of strawberry farmers, you might not sell enough to make a profit. With statistical models, farmers can use demand to precisely calculate the proper amount of crops to plant.
Self Check
In this scatter plot, which sentence best describes how the two variables are related?
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As hot dog prices go up, soft drink prices go down.
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At different locations, as hot dog prices increase, small soda prices also increase.
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Hot dog prices and small soft drink prices are not related.
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The more hot dogs that are bought, the more sodas that are bought.
Additional Resources
Causal Relationships
A panel is rating different kinds of potato chips. The scatter plot below shows the relationship between their average rating and the price of the chips, along with the line of best fit. How could the variables be related?
As the price of a bag of chips in dollars increases, the average rating of the bag of chips in points increases.
Does this represent a causal relationship or simply an association?
In this situation, the independent variable, price, does not seem to cause the rating a person gives the chips. While there appears to be a positive association, there are other factors that may cause the ratings for a bag of chips to go up. For instance, advertising on tv or social media might cause a particular kind of chip to increase in ratings without a change in their price.
Try it
Try It: Describing a Relationship Using a Scatter Plot
The scatter plot shows a strong relationship. How could the variables be related?
Compare your answer:
Your answer may vary, but here is a sample. As a car gets older, it is expected to have been driven more and have more miles on it as the years go by.