A correlation coefficient is a number that quantifies a type of correlation and dependence, meaning statistical relationships between two or more values in fundamental statistics.
Types of correlation coefficients include:
Pearson product-moment correlation coefficient, also known as r, R, or Pearson's r, a measure of the strength and direction of the linear relationship between two variables that is defined as the (sample) covariance of the variables divided by the product of their (sample) standard deviations.
Intraclass correlation, a descriptive statistic that can be used when quantitative measurements are made on units that are organized into groups; describes how strongly units in the same group resemble each other.
Rank correlation, the study of relationships between rankings of different variables or different rankings of the same variable
Spearman's rank correlation coefficient, a measure of how well the relationship between two variables can be described by a monotonic function
Kendall tau rank correlation coefficient, a measure of the portion of ranks that match between two data sets.
Goodman and Kruskal's gamma, a measure of the strength of association of the cross tabulated data when both variables are measured at the ordinal level.
