chapter3

# chapter3 - Relationships PSLS chapter 3 2009 W.H Freeman...

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Relationships   Scatterplots and correlation PSLS chapter 3 © 2009 W.H. Freeman and Company

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Objectives (PSLS chapter 3) Relationships: Scatterplots and correlation Explanatory and response variables Displaying relationships: scatterplots Interpreting scatterplots Adding categorical variables to scatterplots Measuring linear association: correlation Facts about correlation
Student Number of Beers Blood Alcohol Level 1 5 0.1 2 2 0.03 3 9 0.19 6 7 0.095 7 3 0.07 9 3 0.02 11 4 0.07 13 5 0.085 4 8 0.12 5 3 0.04 8 5 0.06 10 5 0.05 12 6 0.1 14 7 0.09 15 1 0.01 16 4 0.05 Here we have two quantitative variables for each of 16 students. 1. How many beers they drank, and 2. Their blood alcohol level (BAC) We are interested in the relationship between the two variables: How is one affected by changes in the other one?

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Student Beers BAC 1 5 0.1 2 2 0.03 3 9 0.19 6 7 0.095 7 3 0.07 9 3 0.02 11 4 0.07 13 5 0.085 4 8 0.12 5 3 0.04 8 5 0.06 10 5 0.05 12 6 0.1 14 7 0.09 15 1 0.01 16 4 0.05 Scatterplots In a scatterplot one axis is used to represent each of the variables, and the data are plotted as points on the graph.
Explanatory number of beers Response BAC x y Explanatory and response variables A response (or dependent) variable measures or records an outcome of a study. An explanatory (or independent) variable may explain changes in the response variable. When there is an obvious explanatory variable, it is plotted on the x axis. Do calories explain sodium amounts?

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Interpreting scatterplots After plotting two variables on a scatterplot, we describe the relationship by examining the form , direction , and strength of the association. We look for an overall pattern …
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chapter3 - Relationships PSLS chapter 3 2009 W.H Freeman...

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