incidence vs relative frequency

incidence and relative frequency both are nouns.

Word	Noun	Adjective	Verb	Adverb
incidence	Yes	No	No	No
relative frequency	Yes	No	No	No

As nouns, relative frequency is a hypernym of incidence; that is, relative frequency is a word with a broader meaning than incidence:

incidence: the relative frequency of occurrence of something
relative frequency: the ratio of the number of observations in a statistical category to the total number of observations

Other hypernyms of incidence include frequency.

incidence (noun)	relative frequency (noun)
the striking of a light beam on a surface	the ratio of the number of observations in a statistical category to the total number of observations
the relative frequency of occurrence of something