15th February 2024

Tests of correlation

Correlation is the measure of the linear relationship between two variables. It is measured using correlation coefficients. 

Pearson’s correlation coefficient

Pearson’s correlation coefficient assumes that one or both variables are normally distributed. The correlation coefficient ranges from -1 to +1.

• Values below 0 denote a negative correlation between variables (one variable decreases as another increases).
• A value equal to 0 denotes no correlation between the two variables.
• Values above 0 denote a positive correlation between variables (one variable increases as another increases).

A correlation coefficient may have a high value (strong correlation) but is statistically insignificant. The statistical significance of a correlation coefficient is based on its corresponding p-value.

Spearman’s rank correlation/Kendall’s rank correlation

Spearman’s rank correlation and Kendall’s rank correlation are non-parametric equivalents of Pearson’s correlation coefficient.