13_corr_reg - CorrelationandRegression...

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    Correlation and Regression
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    Correlation Coefficient aka Pearson Product-Moment Correlation Coefficient. Correlation coefficient summarizes the relations b/t 2 variables, both direction and degree (closeness). Scattergram summary. Sample r; population ρ (Greek rho). Can take values from –1 thru 0 to +1. Sign tells direction (+ or -); magnitude or value tells closeness or degree.
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    Positive Correlation 75 72 69 66 63 60 Height 210 180 150 120 90 Weight Plot of Weight by Height N Ht. In. Wt. Lbs. 1 60 102 2 62 120 3 63 130 4 65 150 5 65 120 6 68 145 7 69 175 8 70 170 9 72 185 Example of a Positive Correlation 10 74 210 When one variable increases, the other also increases.
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    Negative Correlation 400 300 200 100 0 Study Time 30 20 10 0 Errors Plot of Errors by Study Time N Study Time Minutes # Error 1 90 25 2 100 28 3 130 20 4 150 20 5 180 15 6 200 12 7 220 13 8 300 10 9 350 8 Example of a Negative Correlation 10 400 6 When one variable increases , the other decreases .
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    Zero Correlation 1.9 1.8 1.7 1.6 1.5 Toe Size 700 600 500 400 SAT-V Plot of SAT-V by Toe Size N SAT- V Toe Size 1 450 1.7 2 480 1.8 3 500 1.6 4 510 1.8 5 520 1.9 6 550 1.7 7 600 1.6 8 630 1.7 9 650 1.9 Example of a Zero Correlation (*Strictly speaking, no linear relation.) 10 700 1.7 No relation*: when one variable increases , the other variable neither increases nor decreases.
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    Correlation Sign & Magnitude The sign indicates the direction of the relationship. If positive, they increase together. If negative, when one goes up the other goes down. The absolute value tells the strength of the relationship. Values close to +1 and –1 indicate very strong relations. As r 0, the relationship is weaker.
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This note was uploaded on 05/21/2011 for the course PSY 3204 taught by Professor Brannick during the Spring '10 term at University of South Florida - Tampa.

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13_corr_reg - CorrelationandRegression...

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