incidence vs prevalence

incidence

noun
  • A measure of the rate of new occurrence of a given medical condition in a population within a specified period of time. 

  • The act of something happening; occurrence. 

  • The falling of a point on a line, or a line on a plane. 

  • The striking of radiation or a projectile upon a surface. 

  • The manner of falling; bearing or onus, as of a tax that falls unequally. 

  • The extent or the relative frequency of something happening. 

prevalence

noun
  • The total number of cases of a disease in a given statistical population at a given time, divided by the number of individuals in that population. 

  • The quality or condition of being prevalent; wide extension or spread. 

How often have the words incidence and prevalence occurred in a corpus of books? (source: Google Ngram Viewer )