Irish Traveller vs Traveller

Irish Traveller

noun
  • A member of a particular nomadic ethnic minority in Ireland, the Pavee. 

Traveller

noun
  • a member of a nomadic ethnic minority in Norway 

  • Irish English standard spelling of Irish Traveller.; A member of a nomadic ethnic minority in Ireland. 

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