lecture_2_2

# lecture_2_2 - Looking at data relationships Correlation IPS...

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Looking at data: relationships   Correlation IPS chapter 2.2 Copyright Brigitte Baldi 2005 ©

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Objectives (BPS chapter 2.2) Correlation The correlation coefficient “r” R does not distinguish x and y R has no units R ranges from -1 to +1 Influential points
The correlation coefficient is a measure of the direction and strength of a linear relationship between two quantitative variables x and y. The correlation coefficient "r" Student (i) IQ score (x) Self- Concept Score (y) i=1 x 1 = 110 y 1 = 58 i=2 x 2 = 124 y 2 = 72 i=3 x 3 = 126 y 3 = 80 Correlation can only be used to describe quantitative variables. Categorical variables don’t have means and standard deviations. r? of value the is What 14 . 11 s , 70 72 . 8 s , 120 y x = = = = y x

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“r” does not distinguish x & y The correlation coefficient, r, treats x and y symmetrically. r = -0.75 r = ?
“r” does not distinguish x & y The correlation coefficient, r, treats x and y symmetrically.

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