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Section 6.1: Scatterplots and Correlation (Day 1)

Section 6.1: Scatterplots and Correlation (Day 1). Scatterplots. A graph of points which show the relationship between two quantitative variables measured on the same individual (ex., the temperature outside vs. the amount of gas consumed to heat a house). Scatterplots.

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Section 6.1: Scatterplots and Correlation (Day 1)

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  1. Section 6.1:Scatterplots and Correlation (Day 1)

  2. Scatterplots • A graph of points which show the relationship between two quantitative variables measured on the same individual (ex., the temperature outside vs. the amount of gas consumed to heat a house).

  3. Scatterplots • The value for the x-axis is called the explanatory variable and is the independent variable for the data. • The value for the y-axis is called the response variable and is the dependent variable for the data. • This is an example of a scatterplot which is “negatively associated”.

  4. Scatterplots • So, on the previous example, the temperature outside (explanatory variable) explains the amount of gas used to heat the house (response variable). • The colder the temperature, the more gas used; the warmer the temperature, the less gas used. • How could a similar situation be changed to a positive association?

  5. Scatterplots • The explanatory variable here is IQ Test Score • The response variable here is School GPA • This is an example of a scatterplot with Positive Association • A, B, and C could represent Outliers

  6. Describing Scatterplots • Strength • Strong—points follow a tight pattern. • Weak—points are scattered widely. • Form • Straight-line (linear) • Curved • Direction • Positively associated • Both variables increase in value, or both variables decrease in value. • Negatively associated • One variable increases in value, while second variable decreases in value.

  7. Correlation • Describes the direction and strength of a straight-line relationship between two quantitative variables. You cannot calculate correlation for curved graphs. • Usually written as “r”. • The range for correlation is -1 to +1 (remember your crossword puzzle ) • A positive “r” denotes a positive association; a negative “r” denotes a negative association.

  8. Correlation • The closer the number is to -1 or +1, the stronger the correlation. • The closer the number is to 0, the weaker the correlation (or no correlation).

  9. Correlation Examples

  10. Homework • Pages 337..345 #3, 4, and 6

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