A number that is a measure of the strength and direction of
the correlation between two variables.
Correlation coefficients are expressed using the variable r,
where r is
between 1 and –1, inclusive.
The closer r is to 1 or –1, the less scattered the
points are and the stronger the relationship. Only data points
with a scatterplot which is a
perfectly straight line can have r = –1
or r =
1. When r < 0 the data have a negative
association, and when r > 0 the
data have a positive
Least squares regression line