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Maurice Kendall developed methods for rank-based statistical comparison and helped organize statistical theory through influential textbooks. His 1938 paper introduced a measure of rank correlation associated with the Kendall rank correlation coefficient.^[ref]

The coefficient compares pairs of observations: agreement between their two orderings counts positively, disagreement negatively. This makes it a measure of ordinal association rather than a measure of linear agreement in the original measurement units. For data without ties, identical orderings give coefficient one and reversed orderings minus one. Later editions of his textbook series were developed by authors including Alan Stuart, connecting probability distributions, sampling theory and inference.^[ref]