OVERVIEW: The correlation coefficient, r, is a number that "measures the strength and direction of the linear relationship between two quantitative variables. r assumes values between 1 and 1, inclusive. The formula for r is shown below.
r = [1/(n1)]sum[(x x)(yy)/(s_{x}s_{y})]where n is the number of pairs (x,y),
xis the mean of the x values, s_{x} is the standard deviation of the x values, etc.
It should be noted that the formula for r uses standardized
observations (x x)/s_{x} and (y
y)/s_{y}, and that these standardized values
have no units.
Using the TI83, this can be done very easily with a histogram or a boxplot. For two variable data, a scatterplot should be shown.

Here are some Algebra II scholars illustrating the concept of correlation with their textbooks. What are they demonstrating? (A) Correlation r close to 1. (B) Correlation r close to 1. (C) Correlation r close to 0.
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