The Difference Between The Correlation Coefficient and Spearman's Rank Correlation Coefficient
The correlation coefficient, also called Pearson's correlationcoefficient and labelledteststhe goodness of fit of a set of points to a straight line.isbetween -1 and 1.Ifthepoints are a perfect fit to a straight line with a positivecorrelation and iftheyare a perfect fit to a line with a negative correlation.
Spearman's rank correlation coefficientonlytests if tow quantities increase or decrease together, withoutnecessarily being a good fit to a straight line. A value of 1formeansthat if one quantity increases then so does the other with absolutecertainty.
Spearman's rank correlation coefficient is preferable is twoquantities are related but the relationship is not linear. It isusual to draw a graph before assessing the nature of anyrelationship.