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# handout_2_2 - 2.2 Correlation scatterplots display the...

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Correlation scatterplots display the relationship between two variables linear (straight-line) 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 x -values are x and s x . The mean and standard deviation of the y -values 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 - = ) ( y i s y y

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## This note was uploaded on 02/23/2011 for the course STAT 2700 taught by Professor Bill during the Spring '11 term at Adelphi.

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handout_2_2 - 2.2 Correlation scatterplots display the...

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