shrinkage vs drop-off

shrinkage and drop-off both are nouns.

Word	Noun	Adjective	Verb	Adverb
shrinkage	Yes	No	No	No
drop-off	Yes	No	No	No

As nouns, drop-off is a hypernym of shrinkage; that is, drop-off is a word with a broader meaning than shrinkage:

Other hypernyms of shrinkage include decrease, lessening.

shrinkage (noun)	drop-off (noun)
the act of stealing goods that are on display in a store	a change downward
the amount by which something shrinks	a steep high face of rock
process or result of becoming less or smaller	a noticeable deterioration in performance or quality