special interest vs special interest group

special interest

noun
  • A particular political issue that is the focus of political advocacy. 

  • A topic of particular interest and passion, particularly for an autistic person. 

  • A shadowy group with political power. 

  • Used other than figuratively or idiomatically: see special, interest. 

special interest group

noun
  • An advocacy group. 

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