Ayushi,

As it's said :"Sometimes there doesn’t exist a marked linear relationship between two random variables but a monotonic relation (if one increases, the other also increases or instead, decreases) is clearly noticed. A Pearson’s Correlation Coefficient evaluation, in this case, would give us the strength and direction of the linear association only between the variables of interest. Herein comes the advantage of the Spearman Rank Correlation methods, which will instead, give us the strength and direction of the monotonic relation between the connected variables."

For you to find out the correlation there need to be two set of variable series which would be ranked. For example Dx and Dy. For the given example, Individual 1,2,3...n have Dx but what about Dy ?