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lecture7_2slides - Statistics 528 Lecture 7 Section 2.2...

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Statistics 528 - Lecture 7 1 Statistics 528 - Lecture 7 Prof. Kate Calder 1 Section 2.2 - Correlation Statistics 528 - Lecture 7 Prof. Kate Calder 2 Sometimes it is difficult to judge the strength of a relationship by eye => need a numerical measure of strength to supplement a scatterplot CORRELATION (r) - measures the strength and direction of the linear relationship between two quantitative variables. where and are the means of the x -values and y -values, respectively, and s x and s y are the corresponding standard deviations. ° = ± ± ± ² ³ ´ ´ ´ µ - ± ± ² ³ ´ ´ µ - ± ² ³ ´ µ - = n i y s y i y x s x i x n r 1 1 1 x y
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Statistics 528 - Lecture 7 2 Statistics 528 - Lecture 7 Prof. Kate Calder 3 Correlation is an “average” of the product of the standardized values of the two variables. The sign of r gives the direction of the relationship. r > 0 => positive association r < 0 => negative association Strength is on a scale 0 to 1.
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