Now that you know how to run your well-crafted search strategies in the databases of your choice, it's time to think a little bit outside of the published literature world. As I mentioned in the introductory video of this series of tutorials, an exhaustive literature search, especially one that leads to a systematic review, needs to include searches in gray literature. The primary rationale for including relevant gray literature is to overcome, or at least minimize, publication bias, or reporting bias. A lot of scientifically valid studies, especially those with negative results, may never be published. If your systematic review, especially one about the effectiveness of a therapeutic intervention, is based solely on published literature, which tends to report positive results, your review conclusion will be more likely to exaggerate the effectiveness of the intervention. In a lot of cases, that exaggeration can be significant. Gray literature is defined as "information produced on all levels of government, academics, business, and industry in electronic and print formats not controlled by commercial publishing--that is, where publishing is not the primary activity of the producing body." The usefulness of gray literature varies by topic. We've already seen that it is particularly important for reviews of research on therapeutic interventions, where the exclusion of gray literature could mean an exaggeration of effectiveness. Gray literature is important in areas where there is little published evidence, or where a lot of evidence is hidden. Gray literature is especially helpful if the topic of the review is new or changing. Gray literature is useful if the topic of the review is interdisciplinary. Alternative medicine is an area where gray literature is very useful. Depending on your topic, gray literature can be inefficient to search. A big category of gray literature for clinical research is information about clinical trials--especially ongoing trials, and trials with negative results. You can find clinical trial information from a variety of trial registries and results databases. For example, clinical trials.gov is a U. S. government resource that provides trial information, and sometimes results and outcomes, of both publically and privately supported clinical studies conducted in the United States and other countries. Studies are generally registered with the clinical trials.gov when they begin, and information is updated throughout the study. Even though clinicaltrials.gov does not contain all clinical studies conducted in the United States, because not all studies are required by law to be registered, the number of studies registered each year has increased over time as more policies and laws requiring registration have been enacted, and as more sponsers and investigators voluntarily register their studies. Governments of other countries may also sponsor similar resources. The World Health Organization has an international clinical trials registry platform, too. Governments may also make available information about current, publicly funded research activities. For example, the NIH's Research Portfolio online reporting tools provides access to reports, data, and analyses of NIH research activities. Non-government sponsored clinical trial registries and aggregated search platforms are also available, such as "Current Control Trials", and "CenterWatch". The pharmaceutical industry, a primary producer of clinical trials on drugs, also has their own trial databases, such as the Clinical Trials Portal of the International Federation of Pharmaceutical Manufacturers and Associations. Conference proceedings are another area of gray literature that you may want to explore for your review. A well-known resource for proceedings is the Web of Knowledge Conference Proceedings database. From the main search interface, you can see that it automatically includes the conference proceedings citation indices for sciences, social sciences, and humanities. The indices date back to 1991. Valid scientific evidence may also be found in dissertations and theses, which are not always consistently indexed in bibliographic databases. In which case, a specialty database such as the ProQuest Dissertations and Theses should be searched. Studies have also suggested that a search in general scholarly search engines, such as Google Scholar, is more likely to find gray literature than bibliographic databases such as MedLine and Embase, which are primarily indices of published literature. How to find how efficient it is to find useful gray literature for your review really depends on your review topic. The list of resources mentioned above in this video is by no means complete. In general, you should look for relevant government agencies, academic institutions, and relevant business and industries which may release information not otherwise reported and published. literature. In some cases, your gray literature search may be extremely time consuming, but very unrewarding. It may not turn up any evidence. In other cases, you will only find low quality evidence--which may not contain any useable data for your review. Like every aspect of a systematic search in the health science literature, it is best to team up with a medical librarian when conducting searches in gray literature. Thanks for watching--I'll see you next time.