The source for the tabular data is the American Library Association’s (ALA) Office for Intellectual Freedom (OIF). The OIF tracks book challenges and censorship attempts in libraries. The data in the table is from the OIF’s annual report on book challenges.

The OIF defines a book challenge as “an attempt to remove or restrict access to a book or other library material because of its content or viewpoint.” The OIF does not track successful challenges, only challenges that are made.

The OIF’s data is based on reports from libraries and other organizations. The data is not comprehensive, and it is likely that there are many more challenges that go unreported.

The OIF’s data is important for tracking book challenges and censorship attempts. The data can be used to identify trends in challenges, understand the reasons for challenges, and advocate for the right to free speech.