A correlation is a relationship between two variables. 

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Presentation transcript:

A correlation is a relationship between two variables.  A correlation is a relationship between two variables.  In this section we care about linear correlations, which means relationships that can be approximated by linear functions.

Correlation Coefficient . Measures the strength of Correlation Coefficient  Measures the strength of a linear relationship  Tells how close to being in a perfect line the points are.  Also tells whether the general trend is upward of downward.

The correlation coefficient is denoted by the letter r. • The correlation coefficient is denoted by the letter r. • r is always between -1 and 1 (inclusive) • In a perfect correlation r = 1 or r = -1 • If there is no correlation, r = 0.

Typically r = .5 is the dividing line between strong and weak correlations.

If there is a definite pattern, but that pattern isn’t a line, r = 0 (or is close to it).

To find “r” on a graphing calculator, first (1 time only) go press 2nd – 0 (CATALOG)

Scroll through the choices until you find “DiagnosticOn” Scroll through the choices until you find “DiagnosticOn”. Press ENTER twice.

Once you have done this, the Linear Regression (feature (STAT – CALC – #4) we did before will calculate “r”.

Important … Correlation does not mean causation.  Important … Correlation does not mean causation.  Just because there is a correlation between variables, it doesn’t mean one causes the other.