Spearman’s rank correlation coefficient is a statistical measure that assesses the strength and direction of the relationship between two variables based on their ranks rather than their actual values. It evaluates how well the relationship between the two variables can be described using a monotonic function, meaning that as one variable increases or decreases, the other variable tends to do the same (or the opposite). The values of Spearman's coefficient range from -1 to 1, where +1 indicates a perfect positive correlation (both variables increase together), -1 indicates a perfect negative correlation (one variable increases while the other decreases), and 0 indicates no correlation. This method is particularly useful when the data does not meet the assumptions of normality required for Pearson’s correlation.