# What type of correlation coefficient should I be using?

o   Pearson correlation coefficients are used to determine the linear correlation between two continuous variables.  The Pearson correlation coefficient can range from -1 to 1, with negative values indicative of an inverse relationship between the two variables, and positive values indicative of a positive relationship between the two variables.  The square of the Pearson correlation coefficient is called the proportion of variation, and represents the proportion of variation in one variable that is attributable to variation in the second variable.

o   What happens, though when we do not expect linear relationships, or we do not have continuous (interval/ratio) variables?  The interpretation of the Spearman coefficient is only with regard as to whether a relationship exists, but does not indicate whether the association is linear.  The Spearman coefficient has a range of -1 to 1, with negative values indicative of an inverse relationship between the two variables, and positive values indicative of a positive relationship between the two variables.