strength vs validity

strength

noun
  • The quality or degree of being strong. 

  • The intensity of a force or power; potency. 

  • The strongest part of something; that on which confidence or reliance is based. 

  • A positive attribute. 

validity

noun
  • The state of being valid, authentic or genuine. 

  • The genuinity - as distinguished from the efficacity or the regularity - of a sacrament as a result of some formal dispositions being fulfilled. 

  • State of having legal force. 

  • A quality of a measurement indicating the degree to which the measure reflects the underlying construct, that is, whether it measures what it purports to measure (see reliability). 

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