Unless the subject matter is considered common knowledge, citations are necessary when writing about:

Citations are essential in research writing to acknowledge the contributions of other scholars and to maintain academic integrity. When discussing ideas, methodologies, or data from other authors, proper citation gives credit to the original source, allowing readers to trace the development of those ideas and verify the information presented. This practice also upholds the standards of scholarly communication and prevents plagiarism, ensuring that original authors are recognized for their work.

Furthermore, including citations for your own previously published ideas, methodologies, or data is also crucial. This transparency enables readers to understand the context and evolution of the research and helps avoid any misrepresentation regarding the originality of the work. Citing your previous contributions shows the progression of your research and demonstrates respect for intellectual property, reinforcing the ethical standards expected in responsible conduct of research.

The other options do not fully encompass the breadth of what requires citation, either limiting it to specific elements or excluding important aspects of acknowledging prior work.