When you encounter any kind of source, consider:
- Authority - Who is the author? What is their point of view?
- Purpose - Why was the source created? Who is the intended audience?
- Publication & format - Where was it published? In what medium?
- Relevance - How is it relevant to your research? What is its scope?
- Date of publication - When was it written? Has it been updated?
- Documentation - Did they cite their sources? Who did they cite?
From Evaluating Resources at University of California, Berkeley.