compliment vs pat on the back

compliment

verb
  • To pay a compliment (to someone); to express a favourable opinion (of someone). 

noun
  • An expression of praise, congratulation, or respect. 

  • Complimentary language; courtesy, flattery. 

pat on the back

verb
  • To praise or congratulate. 

noun
  • Praise, congratulations. 

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