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Scatterplots & Correlation

Scatterplots & Correlation. Section 3.1A. Relationships between two Variables. A study found that short women are more likely to have heart attacks than tall women…. Smokers on average die younger than nonsmokers….

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Scatterplots & Correlation

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  1. Scatterplots & Correlation Section 3.1A

  2. Relationships between two Variables • A study found that short women are more likely to have heart attacks than tall women…. • Smokers on average die younger than nonsmokers…. • But – to make these conclusions we must first eliminate the effect of other variables.

  3. Lurking Variables • Can strongly influence the relationship between two variables.

  4. Case of the Missing Cookies

  5. Variables • Response Variable • Measures the outcome of a study. • It’s the dependent variable. • Explanatory Variable • May help explain or influence changes in a response variable. • It’s the independent variable.

  6. Identify the explanatory and response variable. • How does drinking beer affect the level of alcohol in our blood? The legal limit for driving in all states is 0.08%. In a study, adult volunteers drank different numbers of cans of beer. Thirty minutes later, a police officer measured their blood alcohol levels.

  7. Identify the explanatory and response variable. • The National Student Loan Survey provides data on the amount of debt for recent college graduates, their current income, and how stressed they feel about college debt. A sociologist looks at the data with the goal of using amount of debt and income to explain the stress caused be college debt.

  8. Scatterplot • Used to show the relationship between two quantitative variables measured on the same individuals. Each individual in the data appears as a point in the graph. • Explanatory variable goes on the horizontal axis. • If there is no explanatory variable then either variable can go on the horizontal axis.

  9. The following data represents 9th grade students who go on a backpacking trip.

  10. Has the increase been constant?

  11. Interpreting Scatterplots • Look for direction (positive, negative, none) • Look at the form of the relationship • Straight or curved • Any clusters • Look at the Strength • How closely does it follow the form • Look for outliers • Individual value hat falls outside the overall pattern of the relationship

  12. Interpret: Backpack

  13. Types of Correlation

  14. Caution….. Association does not imply causation!

  15. Graph Using a calculator:

  16. Interpret…. Direction Form Strength Outliers

  17. Homework • Page 159 (1-13) odd

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