rank-order correlation coefficient vs rank-difference correlation coefficient

rank-order correlation coefficient and rank-difference correlation coefficient both are nouns.

Word	Noun	Adjective	Verb	Adverb
rank-order correlation coefficient	Yes	No	No	No
rank-difference correlation coefficient	Yes	No	No	No

As nouns, rank-order correlation coefficient and rank-difference correlation coefficient are synonyms defined as:

rank-order correlation coefficient and rank-difference correlation coefficient: the most commonly used method of computing a correlation coefficient between the ranks of scores on two variables

Other synonyms of rank-order correlation coefficient include rank-difference correlation, rank-order correlation.

rank-order correlation coefficient (noun)	rank-difference correlation coefficient (noun)
the most commonly used method of computing a correlation coefficient between the ranks of scores on two variables	the most commonly used method of computing a correlation coefficient between the ranks of scores on two variables