Chapters 14 and 15 Notes

# Chapters 14 and 15 Notes - Chapters 14 and 15(Student...

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Chapters 14 and 15 (Student) 1 Describing Relationships: Scatterplots and Correlations • To understand one variable, we must often look at how it is related to other variables. • Bivariate Data – Consists of the values of two different variables. • Three Combinations of Variable Types – Both categorical – One categorical and one quantitative – Both quantitative Scatterplots • Scatterplots show the relationship between two quantitative variables measured on the same individuals. – The values of one variable appear on the horizontal (x) axis, and the values of the other variable on the vertical (y) axis. – A point represents the data that has been observed for both variables. • The scatterplot shows the relationship between the two variables. Interpreting Scatterplots • Look for the overall pattern and any striking deviations from that pattern. • Describe the overall pattern of the relationship by – Form (linear, curve, scattered, etc) – Direction (positive or negative) – Strength (weak, moderate, or strong) • An outlier is an individual value that falls outside the overall pattern of the relationship.

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Chapters 14 and 15 (Student) 2 Patterns of Association • Two variables are positively associated when larger values of one variable tend to be accompanied by larger values of the other (scatterplot slopes upward as we move from left to right). • Two variables are negatively associated when larger values of one variable tend to be accompanied by smaller values of the other (scatterplot slopes downward from left to right). Scatterplot of Heights and Weights of 8 College Women 80 90 100 110 120 130 140 150 60 61 62 63 64 65 66 67 68 69 70 Height (inches) Weight (pounds) Example: Explore the relationship between the height and weight of college women. Scatterplot of Age and Resale Value of 19 Cars 5 10 15 20 25 30 35 40 123456789 Age (years) Price (x \$100) Example: Explore the relationship between the resale value and the age of used cars.
Chapters 14 and 15 (Student) 3 Example During the cold winter months a restaurant in the Northeast features a hot cereal specially prepared a few hours before opening.

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## This note was uploaded on 06/13/2011 for the course STAT 110 taught by Professor Johnson during the Spring '07 term at South Carolina.

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Chapters 14 and 15 Notes - Chapters 14 and 15(Student...

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