What type of document provides supplemental material relevant to research but is not essential?

The appendix serves as a supportive document that includes additional material relevant to research. While the main text conveys the primary findings and arguments, the appendix contains supplementary information such as raw data, detailed explanations, charts, or questionnaires that contribute to the overall understanding of the research but are not essential for grasping the core message. This allows readers who wish to delve deeper into specific aspects of the research to access pertinent information without interrupting the flow of the main narrative.

In contrast, a bibliography lists the sources consulted during the research process and is essential for demonstrating the breadth of research but does not contain supplemental content. An index provides an organized list of topics and pages in a document for easy navigation and is also crucial, as it aids in quickly locating information. A summary condenses the main ideas and findings but does not offer additional context or details, making it a different function from the appendix.