Documents are produced for a purpose. The purpose may be to inform. It may be to persuade. It may be to sell a product. Perhaps it is trying to get the audience to vote a particular way. The purpose may influence the content to only present one side of an issue.
If you learned that the author of a book about national security was a member of the National Rifle Association, would that enable you to make predictions concerning their probable opinions? What if the author was a member of Amnesty International?
What if a respected medical physician-author wrote a book about epilepsy and worked for a pharmaceutical company? The information presented may be balanced and unbiased but you may wish to know that her employer sold drugs to treat epilepsy and that competing companies offered alternative pharmaceuticals or treatments.
