independent vs item-by-item

independent is a noun but item-by-item is not a noun.

Word	Noun	Adjective	Verb	Adverb
independent	Yes	Yes	No	No
item-by-item	No	Yes	No	No

independent (noun)	item-by-item (noun)
a writer or artist who sells services to different employers without a long-term contract with any of them
a neutral or uncommitted person (especially in politics)

independent (adjective)	item-by-item (adjective)
free from external control and constraint	separate and distinct from others of the same kind
(of a clause) capable of standing syntactically alone as a complete sentence
(of political bodies) not controlled by outside forces
not controlled by a party or interest group