Additional Resources:


Grey Literature (Evidence Rating Element)

Research and evaluations that are not controlled by commercial publishers (i.e., not published in a peer-review journal or a book). Sources of grey literature or unpublished studies include dissertations, theses, government reports, technical reports, conference presentations, and other unpublished sources. This is a dimension in the Practices Scoring Instrument that assesses the extent to which a meta-analysis includes results from unpublished or “grey” literature sources. A meta-analysis should always attempt to include grey literature due to consistent evidence that the nature and direction of research findings is often related to publication status. See Publication Bias for more information.

Note: If the literature search does not include an effort to locate unpublished studies, or is explicitly restricted to published literature, it is not eligible for inclusion as a practice on