The American Library Association (ALA) has tracked book challenges, which are attempts to remove or restrict materials, since 1990. Last year, the ALA recorded 323 reported book challenges in the United States, a 17% increase from the 275 reported challenges in 2015. In most years, about 10% of the reported challenges result in removal or ban from the school or library. However, in 2016, five of the top ten most challenged books were removed. The ALA estimates that only about 18% of challenges are reported to its Office for Intellectual Freedom, meaning that the actual number of attempts to ban books is likely much higher.