In the case of research papers, supporting materials may include surveys, questionnaires, or schematics and the like that were used to produce the results included in the paper.
Because of its supplementary nature, it's important that material in an appendix not be left to speak for itself.
The answer to that really is as long as it needs to be.
The appendix should be streamlined, and not too loaded with information, but there is a lot of flexibility.
The appendix does not count towards the word count for your research paper, so you can set the length to suit.
If you have a very long and complex paper, with an extremely long appendix, it is a good idea to break it down into sections, allowing the reader to find relevant information quickly.
Research papers, including academic and medical studies, usually follow APA style guidelines for the formatting of appendices. For each of these styles, format the appendix as follows: An addendum is new material added to a book or other written work after its first edition has been produced.
For example, an addendum may contain updated research or additional sources that came to light or further explanation about the book from the author. An addendum can change the terms of a contract, such as canceling sections or updating terms or pricing in sections of a contract without the contract becoming null and void in its entirety, which would require all parties involved to read, agree to, and sign it again.
It is usually good practice to include your raw data within the appendix, laying it out in a neat table and allowing anybody to recheck your results.
The tables that you include within the body of the paper will then be concise and uncluttered, allowing the reader to pick out the important information.