Documentary research.

Documentary research is a research method in which people use previously recorded information as their primary source material. This material usually consists of written or digital texts, but it may also include images, videos, audio recordings, and other forms of documentation. This research is generally intended to supplement an academic or scientific study. Documentary researchers must not only locate and access documents; they must also evaluate documents for suitability. Four primary criteria for evaluation are authenticity, credibility, representativeness, and meaning. Only documents that meet these criteria should be considered suitable for use in serious documentary research.