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Unformatted text preview: 3/20/2008 1 Regression Psyc110 March 20, 2008 Outline Correlations contd. Review Hypothesis testing Regression introduction Prediction Regression equation Regression coefficients Accuracy of prediction Correlation Review Scatterplot used to display associations visually Covariance formula: similar to variance, but includes sum of cross-products instead of sum of squares Correlation coefficient = r = standardized covariance Ranges from -1.00 to +1.00 Sign = direction of relationship Value = strength of relationship Positive Negative ? ?? = ? ? ( ? ? ) 1 = ? ?? ? ? 3/20/2008 2 1) Use formulas to calculate cov XY and r XY 2) Compare calculated r to value in Table D.2 df = N-2 Always two-tailed (unless you hear differently) Reject if calculated r is more extreme than tabled r Can be positive or negative (must add minus sign for negative r ) Hypothesis Testing with Correlations As always, using Greek letters to denote hypothesized population values Population correlation coefficient = (rho) For variables X and Y, written as...
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- Spring '08