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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. 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.

  6. Has the increase been constant?

  7. Types of Correlation

  8. Describe the correlation • Apples: circumference, weight • College freshmen: shoe size, weight • People: age, grip strength • Drivers: blood alcohol, reaction time

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

  10. 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

  11. When writing to describe: • There appears to be a (strong, weak, moderate) (positive/negative) (linear, nonlinear) relationship between _____ (give the x variable) and ______ (give the y variable) • Do not just say between x & y!

  12. Graph Using a calculator:

  13. Interpret…. Direction Form Strength Outliers Influential Pt!

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

  15. Interpret: Backpack

  16. Homework • Page 159 (1-13) odd

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