The list is based on a proprietary method that uses sales figures, other data and internal guidelines that are unpublished—how the "Times" compiles the list is a trade secret.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. In 2017, a "Times" representative said that the goal is that the lists reflect authentic best sellers. The list has been the source of controversy over the years. On occasions where the Times believes a book has reached the list in a suspicious way such as through bulk purchases, the book's entry on the list is marked with a dagger symbol (†).