it is always positive, it gives the
strength of the relationship without distinguishing
between positive and negative correlation

it is often thought to give more intuitive
results. For example if R = 0.5 then R^{2}
= 0.25. This would be a weak relationship
and 0.25 seem a better indicator of a
weak relationship than 0.5.

Correlation
and Regression Analysis are
both covered in the MiC Quality
course in AdvancedStatistics