PSY201 11.13.13

# 9 111313 these crossproducts tell you about the

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Unformatted text preview: ulate the cross ­product of Z scores   Cross ­product = mul7plying scores on one variable by scores on another   What happens in the case of a nega1ve correla1on? ▪  If you mul7ply a high Z score (+) by a low Z score ( ­), you get a nega7ve cross ­product ( ­) ▪  If you mul7ple a low Z score ( ­) by a high Z score (+), you get a nega7ve cross ­product ( ­) ▪  If you add up these cross ­products, you get a large nega7ve number ( ­)   In compu7ng a correla7on, we calculate the cross ­product of Z scores   Cross ­product = mul7plying scores on one variable by scores on another   What happens in the case of no correla1on? ▪  Varied associa7ons: high with high, low with low; high with low, low with high ▪  Adding up all of these cross products would result in posi7ve cross ­products and nega7ve cross ­products canceling each other out, given a result of 0, or close to 0. 9 11/13/13   These cross ­products tell you about the direc1on of the rela7onship   Posi7ve vs. Nega7ve   In order to ﬁgure out the strength of the rela7onship in a standard way, need to divide the sum of the cross ­ products by the number of people in the study   This represents the average of the cross ­products of Z scores   Correla7on can range from  ­1 to +1 (with 0 represen7ng no correla7on)   Correla1on coeﬃcient: the resul7ng number when you divide the sum of the cross products of Z score by the number of people in the study   Also called Pearson correla7on coeﬃcient (or the Pearson product ­moment cor...
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