https://bookadreport.com/book-market-overview-authors-statistics-facts/

https://www.thebigthrill.org/2017/09/trend-report-the-state-of-horror-lit/

https://www.reuters.com/article/pat-july-29-books-author-gray/book-talk-vampire-writer-finds-market-isnt-too-cut-throat-idUSSP46825720090729