1.8 Measuring Correlation

The correlation coefficient is the variable we use to measure linear correlations. It takes the letter r and . r tells you everything you need to know about a linear correlation: direction and strength. If then the linear regression will be positive and the closer r gets to 1 the stronger the correlation will be. Similarly, indicates a negative correlation with strength increasing as r approaches -1.

Pearson’s correlation coefficient formula: , where is the standard deviation of the independent variable, is the standard deviation of the dependent variable, and is the covariance of the two.

Covariance:

This formula has been worked out to

Do p.581# ‘Use technology for the correlation coefficient’

Coefficient of Determination (): the coefficient of determination is used to determine the strength of a correlation, regardless of the linearity of it-this means you use to determine the strength of a non-linear correlation, or to determine which non-linear correlation is the strongest.

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