These forms of evidence exist and are equally valid for consideration in an evidence evaluation, although they canвЂ™t be subjected to meta-analysis in a formal systematic review process ( Popay et al.2006). You should also be aware that in very specific circumstances - such as if you need to conduct a narrative synthesis as part of your evidence review - other types of evidence relevant for your guideline might not fit within the boundaries of knowledge as defined above. If you do decide to seek information outside of bibliographic databases, it is important that these decisions are documented in your search strategy along with how you searched, retrieved and considered this information within your guideline. Being able to find it may include actively seeking information from individuals or organisations through interviews or written correspondence.

Unpublished evidence, which may not even be in the public domain - such as unpublished industry data or cultural knowledge, can be challenging to identify. Non-commercial and non-peer-reviewed literature is often referred to as вЂgrey literatureвЂ™ and includes government reports, public health monitoring or surveillance data, and data from clinical trials registries. As an example, there is a high incidence of unpublished data for recommendations involving drugs because results from clinical drug trials are sometimes not reported or published ( BrГ¦nd, Straand, JakobsenВ & Klovning, 2016). Additionally, excluding these data can introduce significant bias ( Adams, SmartВ & Huff, 2017). There is now a recognised need to include unpublished studies and other non-commercial evidence as they can provide a more comprehensive view of the topic. You should aim to find a balance between the sensitivity (the proportion of relevant articles retrieved) and specificity (the proportion of irrelevant articles not retrieved) of your search ( Montori, Wilczynski, MorganВ & Haynes, 2005).Д«ibliographic databases of peer-reviewed literature are the primary source of information on which to base a systematic review. These can be found by searching databases such as the Cochrane Database of Systematic Reviews (CDSR) and the Guidelines International Network (G-I-N) library.Д¬onducting broad searches will ideally capture all relevant evidence, but this process might also identify many studies that are not relevant. Existing reviews and guidelines can save a lot of time and resources as they may address most or all of the questions relevant to your review.

There is an ever increasing body of evidence that can be used to inform guideline recommendations however, before you consider reviewing this evidence you should determine whether there have been previous attempts to review the literature. The quality of systematic reviews will depend on the ability of the reviewer to identify as much relevant evidence as possible.

March networks evidence reviewer