Spearman's rank correlation coefficient measures the strength and direction of a monotonic relationship between two variables. A positive Spearman correlation coefficient indicates an increasing monotonic trend (as one variable increases, the other tends to increase), while a negative Spearman correlation coefficient indicates a decreasing monotonic trend (as one variable increases, the other tends to decrease). For more information see https://en.wikipedia.org/wiki/Spearman%27s_rank_correlation_coefficient#Interpretation.