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Ch. 8: Correlation

Ch. 8: Correlation. Reading a scatterplot – graphical interpretation of the relationship between 2 variables Independent and dependent variables Examples: Mars rocks AAVP data SAT scores vs. essay length Ex. A #6 p.124. Correlation Coefficient ( r )

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Ch. 8: Correlation

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  1. Ch. 8: Correlation • Reading a scatterplot – graphical interpretation of the relationship between 2 variables • Independent and dependent variables • Examples: • Mars rocks • AAVP data • SAT scores vs. essay length • Ex. A #6 p.124

  2. Correlation Coefficient (r) • Measure of linear association (clustering, tightness) • The relationship between 2 variables can be summarized by: • Average of the x-values • SD of x-values • Average of the y-values • SD of the y-values • r

  3. Correlation coefficients are always between -1 and 1. • A positive correlation vs. a negative correlation. • Standard Deviation Line: A line that goes through the point of averages and through all points which are an equal number of SDs away from the average, for both variables. • Slope =

  4. Computing r • Convert each variable to standard units • Take the average of the products • Example: Ex. D #1(a)

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