Spearman's Rank Correlation

https://statistics.laerd.com/statistical-guides/spearmans-rank-order-correlation-statistical-guide-2.php

Definition

The Spearman correlation coefficient, rs, can take values from +1 to -1. A rs of +1 indicates a perfect association of ranks, a rs of zero indicates no association between ranks and a rs of -1 indicates a perfect negative association of ranks. The closer rs is to zero, the weaker the association between the ranks.