When analyzing bivariate data that has a linear relationship, correlation, also know as the correlation coefficient and commonly referred to simply as "r", is used to measure both the:
II. Correlation Examples
EXAMPLE SCATTERPLOTS WITH CORRELATION
III. Correlation Facts
(1) Correlation is a measure of the linear (straight-line) relationship between two variables.
(2) Correlation is calculated using the formula below. It is important to note, however, that correlation is virtually never calculated by hand, and almost always is calculated using technology, such as a statistics enabled calculator or statistics package.
(3) If r is zero or approximately zero, there can be two possible reasons.
(4) Correlation has a range from -1.00 to +1.00 and the sign (positive or negative) of the correlation coeﬃcient indicates the direction (positive or negative) of the linear relationship between X and Y.
(5) If correlation equals -1 or +1:
(6) The magnitude (absolute value, distance from zero) of the correlation coeﬃcient indicates the strength of the
linear relationship between X and Y.
(7) The correlation coeﬃcient (like the mean and standard deviation) can be greatly aﬀected by outliers.
(8) CORRELATION IS NOT CAUSATION!!! Just because X and Y are correlated, it does not mean
that one causes the other.