Grey literature searches are now commonly included in the research methods sections of literature and systematic reviews as way of demonstrating a comprehensive search for information and for addressing publication bias. Grey literature can be obtained from a wide range of sources such as conferences, government, professional and regulatory organisations, trial registries, and various repositories. Searching the grey literature can be a daunting task and therefore requires a strategic approach in which you search those resources that make the most sense for your research question.
Figure 1 illustrates a strategy for locating grey literature as part of the overall research process.1
Once you have performed your grey literature search, good practice is to document the strategy used either as a narrative only, or a narrative that refers to a table of sources, search terms, limiters, search results, excluded results and number of studies included for final consideration.
1 . Adapted from Duffield, A. et al. (2004). "Process to Identify the Grey Literature", Review of the published literature for the impact and cost-effectiveness of six nutrition related emergency interventions, Report prepared by the ENN, p. 49. Available: http://www.unscn.org/layout/modules/resources/files/ENN_literature_review_of_cost-effectiveness_of_6_nutrition_i.pdf