Use Of Spearman Rank Correlation. It assesses how well the relationship between two variables can be described using a monotonic function. Kendalls Tau and Spearmans rank correlation coefficient assess statistical associations based on the ranks of the data.
The Spearmans Correlation Coefficient represented by ρ or by r R is a nonparametric measure of the strength and direction of the association that exists between two ranked variables. It assesses how well the relationship between two variables can be described using a monotonic function. Where is the difference in statistical rank of corresponding variables and is an approximation to the exact correlation coefficient.
Spearmans Rank Correlation When data is not normally distributed or when the presence of outliers gives a distorted picture of the association between two random variables Spearmans rank correlation is a non-parametric test that can be used instead.
In a monotonic relationship the variables tend to change together but not necessarily at a constant rate. The Spearman correlation coefficient is based on the ranked values for each variable rather than the raw data. You can use the color change as a signal. If your data does not meet the above assumptions then use Spearmans rank correlation.
