The meaning of "banned" can be misleading. When I looked into previous "banned books" data sets I found that some of the books were moved up an age level (e.g., from elementary school to high school) which is not what people think of when they hear the word "ban." Others were books that sounded religious in nature (e.g., I recall a book from the Christian publisher, "Zondervan") which is understandable for U.S. public schools.