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Unformatted text preview: 2.2 Correlation scatterplots display the relationship between two variables linear (straightline) relationships are important because they are quite common linear relationship is strong if points lie close to a straight line linear relationship is weak if points are widely scattered about a line Figure 2.9 problem with scatterplot our eyes can be fooled about the strength of the relationship need numerical measure of strength of linear relationship correlation The correlation r measures the strength and direction of the linear relationship between two quantitative variables. Suppose that we have data on variables x and y for n individuals. The mean and standard deviation of the xvalues are x and s x . The mean and standard deviation of the yvalues are y and s y . The correlation r between x and y is: r = 1 1 n  ) ( x i s x x ) ( y i s y y Suppose that x is height in centimeters and y is weight in kilograms and that we have height and weight measurements for n people. ) ( x i s x x is the standardized height for the i th person ) ( y i s y y is the standardized weight for the i th person ) ( x i s x x = ) ( cm cm cm = # with no units ) ( y i s y y = ) ( kg kg kg = # with no units Standardized values have no units of measurement. Standardized values have no units of measurement....
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 Spring '08
 ABDUS,S.

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