CORRELATION

How do we choose a correlation technique? We choose on the basis of the situation that is being examined and the data's level of measurement. Here we will address three techniques, of which two are nonparametric and one is parametric. These procedures are most often found in beginning statistics books, and each serves a different level of measurement, as illustrated by the following table.

Level of Measurement	Correlational Technique	Kind
Nominal	Contingency coefficient	Nonparametric
Ordinal	Spearman rank	Nonparametric
Interval	Pearson product-moment	Parametric

After we choose a correlation technique, we use it to compute a number called a coefficient of correlation. This number tells us the exact strength and direction of the relationship between the two sets of scores. We begin our discussion with the Pearson product-moment coefficient of correlation.