 In recent years it has evolved into multiple lists, grouped by genre and format, including fiction and non-fiction, hardcover, paperback and electronic.The list is based on a proprietary method that uses sales figures, other data and internal guidelines that are unpublished—how the "Times" compiles the list is a trade secret.In 1983 (as part of a legal argument) the "Times" stated that the list is not mathematically objective but rather editorial content.