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Unformatted text preview: 1 Psych 100A Winter 2010 Lecture 13: Correlation and Regression Introduction Linear Correlation Regression Simpl Lin R ssi n Simple Linear Regression Model/Formulas Applications Real-life Applications Practice Problems Internet Resources 1 Correlation Correlation A measure of association between two numerical variables. Example (positive correlation Example (positive correlation) Typically, in the summer as the temperature increases people are thirstier. 2 Specific Example For seven random summer days, a person Temperature (F) Water Consumption (ounces) 75 16 83 20 recorded the temperature and their water consumption, during a three- hour period spent outside. 85 25 85 27 92 32 97 48 99 48 3 How would you describe the graph? 4 How strong is the linear relationship? 5 Measuring the Relationship Pearsons Sample Correlation Coefficient, r measures the direction and the strength of the linear association between two numerical paired variables. 6 2 Direction of Association Positive Correlation Negative Correlation 7 Strength of Linear Association r value Interpretation 1 perfect positive linear relationship no linear relationship-1 perfect negative linear relationship 8 Strength of Linear Association 9 Other Strengths of Association r value Interpretation 0 9 strong association 0.9 strong association 0.5 moderate association 0.25 weak association 10 Other Strengths of Association 11 Formula = the sum n = number of paired items x i = input variable y i = output variable x = x-bar = mean of...
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- Winter '10