15_Lecture15.1_Correlation_0420_Spring11

15_Lecture15.1_Correlation_0420_Spring11 - PSY207B Spring...

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1 PSY207 B Spring 2011 Psychological Statistics Describing Relationships - Correlation – Objectives You should be able to . . . • Describe relationships using correlation • Define and identify: –Positive correlations –Negative correlations –Zero correlations • Construct and interpret scatterplots • Compute and interpret the Pearson Product-Moment Correlation Coefficient Describing Relationships - Correlation – 13.1 Introduction to Correlation Correlation • The degree of relationship between two or more variables • The co-relationship between variables Example • Is there a relationship between height and salary? • Do taller people tend to make more money? • Do taller people tend to make less money? • Is there any relationship at all?
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2 Person Height Salary A 5’7” 24,000 B 5’4” 26,000 C 6’1” 38,000 D 5’10” 33,000 E 6’3” 40,000 ::: Height and Salary Height and Salary Displaying Correlations: Scatter plot • A graph that plots pairs of scores • Values for one variable are plotted on the x axis • Values for the other variable are plotted on the y axis • You choose which variable to plot on which axis Person Height Salary A 5’7” 24,000 B 5’4” 26,000 C 6’1” 38,000 D 5’10” 33,000 E 6’3” 40,000 Salary Height 10,000 15,000 20,000 25,000 30,000 35,000 40,000 45,000 5’ 5’4” 5’7” 5’10” 6’1” 6’3” B A D C E The Characteristics of a Relationship •Direction –positive, negative, none •Strength/consistency –r 2 •Form –Pearson product moment correlation –Spearman correlation A high score on one variable is associated with a high score on the other variable; or, a low score is associated with a low score • There is a direct relationship between the variables Positive Correlation Negative Correlation • A high score on one variable is associated with a low score on the other variable and vice versa
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3 Zero Correlation • There is no relationship • It is equally likely that a high score will be associated with a high or low score
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15_Lecture15.1_Correlation_0420_Spring11 - PSY207B Spring...

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