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Lecture+15+su10+_correlation_

# Lecture+15+su10+_correlation_ - Sociology 210 Lecture 15...

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Sociology 210 Lecture 15: Correlation

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02/23/11 Soc 210 summer 2010 2 Correlation Correlation is a statistical technique used to measure and describe the relationship between two variables measured on an interval-ratio scale. Most common measure of correlation is the Pearson correlation ( r ) Used with two interval/ratio variables Used to measure degree of linear relationship between two variables
02/23/11 Soc 210 summer 2010 3 The Direction of Relationship Positive Correlation : when two variables move in the same direction In other words, higher values of one variable are associated with higher values of the other Negative Correlation : when two variables tend to move in opposite directions In other words, higher values of one variable are associated with lower values of the other

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02/23/11 Soc 210 summer 2010 4 Examples of positive and negative relationships
02/23/11 Soc 210 summer 2010 5 Form: (Linear in our class) Linear association: when points in a scatterplot tend to form a straight line Pearson’s correlation measures how well the data points approximate a linear association Degree How well do the data fit the specific form being considered? Degree is measured by the numerical value of the correlation coefficient Correlations of 1.0 or -1.0 indicate perfect fit A correlation of 0 indicates no fit at all Intermediate values represent the degree to which data points approximate the perfect fit The Form and Degree of a Relationship

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02/23/11 Soc 210 summer 2010 6 Which scatterplot shows the strongest positive linear relationship?
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