in depth vs thorough

in depth

prep
  • Comprehensive, thorough, detailed. 

thorough

noun
  • A furrow between two ridges, to drain off the surface water. 

adj
  • Utter; complete; absolute. 

  • Painstaking and careful not to miss or omit any detail. 

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