article_snippet.sent: seven Harry Potter books have sold more than 450 million copies since the first was published in 1997.
article_snippet.sent: And now researchers have discovered all  seven Harry Potter books success may lie in the use of words author J.K Rowling chose across the series - rather than the texts as a whole.
article_snippet.sent: all  seven Harry Potter books have sold more than 450 million copies and all  seven Harry Potter books success may lie in the use of words used - rather than the texts as a whole.
article_snippet.sent: the researchers from Lancaster University screened all seven Harry Potter novels: Harry Potter and the Sorcerer's Stone (1997), Harry Potter and the Chamber of Secrets (1998), Harry Potter and the Prisoner of Azkaban (1999), Harry Potter and the Goblet of Fire (2000), Harry Potter and the Order of the Phoenix (2003), Harry Potter and the Half-Blood Prince (2005) and Harry Potter and the Deathly Hallows (2007).
article_snippet.sent: Study screened seven Harry Potter novels. 
article_snippet.sent: Researchers screened all seven Harry Potter novels and selected 120 passages, each of which was four lines long and didn't require a high level of familiarity with the books.
highlights_snippet.sent: Researchers chose 120 passages from across all  seven Harry Potter books .
  