Linear Relationship (2 of 2)
It is possible for there to be a completely systematic relationship between the two variables but still no linear
relationship. Consider the scatterplot shown below.
There is a systematic relationship between the two variables, but the relationship
is not linear since a straight line cannot come close to going through the points.
Product Moment Correlation
is the most commonly- used
index of the degree of linear relationship. Spearman's
is another commonly-used measure. Both of these measures range from
1 (for a perfect positive linear relationship) through 0 (for no linear relationship)
to -1 (for a perfectly negative linear relationship (one where the line has a