commendation vs pat on the back

commendation

noun
  • A message of affection or respect; compliments; greeting. 

  • The act of commending; praise; favorable representation in words; recommendation. 

  • That which is the ground of approbation or praise. 

  • An award or recognition for performance; a medal. 

pat on the back

noun
  • Praise, congratulations. 

verb
  • To praise or congratulate. 

How often have the words commendation and pat on the back occurred in a corpus of books? (source: Google Ngram Viewer )