mitigate vs set back

mitigate

verb
  • To downplay. 

  • To reduce, lessen, or decrease; to make less severe or easier to bear. 

set back

verb
  • To delay or obstruct. 

  • To remove from or allow distance. 

  • To install or position behind a boundary or surface, or in a recess. 

  • To cost money. 

  • To reverse, go backwards. 

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