firmness vs strong-mindedness

firmness

noun
  • strictness; mental strength 

  • security; steadfastness; good grip 

  • physical durability; rigidness (of material) 

strong-mindedness

noun
  • the state or quality of being strong-minded. 

How often have the words firmness and strong-mindedness occurred in a corpus of books? (source: Google Ngram Viewer )