certification vs corroboration

certification

noun
  • The act of certifying. 

  • The granting of a certificate. 

  • A professional qualification that certifies a person's ability. 

corroboration

noun
  • The act of corroborating, strengthening, or confirming; addition of strength; confirmation 

  • That which corroborates. 

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