Who are Young Adults and what are Their reading Preferences?

According to Rosemary Chance's book Young Adult Literature in Action , the American Library Association defines young adults as ages 12-18.  In my survey of  students, I found that none of the students had the same favorite book.  I interviewed 16 and 17 year old students.  The books were also of several different genres : A Walk to Remember, Harry Potter, Last Song, The Fountain Head, The Color Purple, and Pete Rose.  Two of the students said their favorite book was also the last book they read.  I interviewed 2 boys.  One chose Harry Potter and the other Pete Rose as their favorite books. Both boys had last read for pleasure a book about athletes (Derek Jeter and Hakeem Olajuwon).  None of the girls listed nonfiction books.