nurse practitioner vs registered nurse

nurse practitioner

noun
  • A professional nursing designation recognized in some jurisdictions, denoting an individual who is fully qualified as a nurse and who has additional qualifications and authorization to provide diagnoses and/or treatments, including writing prescriptions . 

registered nurse

noun
  • A professional nurse who is a licensed graduate of a university or college of nursing who has successfully passed an examination such as NCLEX-RN. 

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