Information that can be found in academic journals and textbooks – particularly the findings from sound research and evaluations that are relevant to the problem or opportunity of interest – have traditionally been the key source of evidence that is emphasized.
Evidence can also be found in the “grey” literature which includes things like reports, working papers, newsletters, government documents,
white papers and evaluation reports. These are often produced by government and non-government agencies to report on their activities or to share their ideas and information. Because this literature doesn’t go through a peer-review process it can be more current than academic research; however, because it’s not peer-reviewed, the quality of grey literature can be variable.