Appendices provide authors an opportunity to present detailed data or other information that would be distracting to the reader if kept in the main text. There are not many guidelines in what to include in an appendix as this varies greatly from one field to another. In addition, because the content varies greatly, there are few guidelines for formatting.
For more information, consult Section 2.14 of the APA Manual (7th ed.) and pages 6–7 of the Saybrook Handbook of Format and Style, attached below.
Many authors struggle with choosing where to place certain pieces of information. As this varies greatly from one document to the next, there is no “one size fits all" answer. As mentioned above, material that should be placed in appendices, in general, would be a distraction to the reader when placed in the main text. For some documents, appendices are a good way to inform the reader about specific details without disrupting the flow of the writing. When deciding where to place information, use these guiding questions: