Spearman's rank correlation coefficient

Spearman's rank correlation coefficient is Pearson's correlation coefficient on the ranks of the observations. It is a non-parametric measure for rank correlation. It assesses the strength of the association between two ranked variables. Ranked variables are ordinal numbers, arranged in order. First, we rank the observations and then compute the correlation of ranks. It can apply to both continuous and discrete ordinal variables. When the distribution of data is skewed or an outlier is affected, then Spearman's rank correlation is used instead of Pearson's correlation because it doesn't have any assumptions for data distribution.