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Lab9_corr - Lab 9 Correlation Regression Learning...

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1 Lab 9 Correlation & Regression Learning Objectives Compute correlations and regression lines by hand and by SPSS. Understand the meaning and uses of correlation & regression. Understand the limits of study designs in which the IV is not manipulated. Part 1: Correlation Describing the correlation Long name: Pearson product-moment correlation coefficient. Aka “Pearson’s r” aka “correlation coefficient.” Notation. Numerical summary of joint distribution labeled r in the sample and rho ( ) in the population. Single number that summarizes a scatterplot. Purpose – tells the form and magnitude of relations between 2 variables. ρ
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2 Properties of r The range of r is form –1 thru 0 to +1. The sign of r tells the direction of relations between the 2 vbls. The magnitude of r tells how closely the 2 vbls are related. See handout 1. Positive Correlations 30 20 10 0 Hours Studied 100 90 80 70 60 Grades Positive Correlation 30 27 24 21 18 15 Hours Studied 100 90 80 70 60 Grades Positive Correlation r = 1 As study time increases, test scores improve. If we had a perfect relationship between study time and test scores, we would see r = 1 (right graph).
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