headship vs premiership

headship

noun
  • The position of a head or chief. 

  • The position of a headmaster or headmistress. 

premiership

noun
  • The office of a premier or prime minister. 

  • The position held by the champion team at the end of a particular season (especially as used in Australian rules football). 

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