PSY201 11.13.13

Z score number of standard devia7ons that a score is

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Unformatted text preview: inear correla7ons:   Large/Strong: dots call close to a straight line   Small/Weak: dots fall far from a straight line (harder to see a “pa`ern” 6 11/13/13 h`p://www.youtube.com/watch?v=VFjaBh12C6s   Compu7ng a correla1on coeﬃcient: a sta7s7c that gives you the exact correla7on in terms of its direc2on and strength   We want to ﬁgure whether highs on one variable go with highs on another… thus we need a way to compare variables   But how do we do this when we have two variables that are measured on diﬀerence scales? 7 11/13/13   Z scores!   Z score = number of standard devia7ons that a score is from the mean   Conver7ng to Z scores is a way to “standardize”   A raw score that is high (above the mean) will always have a posi7ve Z score   A raw score that is low (below the mean) will always have a nega7ve Z score   Z scores tell you how far above or below the mean a par7cular score was   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 a posi1ve correla1on? ▪  If you mul7ply a high Z score (+) by a high Z score (+), you get a posi7ve cross ­product(+) ▪  If you mul7ple a low Z score ( ­) by a low Z score ( ­), you get a posi7ve cross ­product (+) ▪  If you add up these cross ­products, you get a large posi7ve number (+) 8 11/13/13   In compu7ng a correla7on, we calc...
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