THE BIVARIATE CORRELATION COEFFICIENT: FROM CONCEPT TO APPLICATION

The bivariate correlation coefficient is among the most fundamental and widely applied measures in statistical analysis, offering a quantitative assessment of the association between two continuous variables. This brief review revisits the essential concept of correlation, distinguishing the tendency of variables to vary together from the frequently misunderstood notion of causation. Its practical value is demonstrated through a biomedical example involving two hematological variables. Particular emphasis is placed on Pearson’s product-moment correlation coefficient (r), with attention to its computation, underlying assumptions, and interpretation. The discussion also contrasts Pearson’s r with Spearman’s rank correlation coefficient (ρ), clarifying their appropriate use for data following normal and non-normal distributions, respectively.