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World Gastroenterology Organisation
World Gastroenterology Organisation
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Graded Evidence

WGO's 'Graded Evidence' system is built to help Member Societies of Gastroenterology, and all those interested in the practice and research of gastroenterology, keep track of the literature in topics covered by WGO Guidelines. Most guidelines are based on evidence which is out of date as they appear. Sometimes the 'lag time' is as much as two to three years. WGO's Graded Evidence system bridges this gap. WGO Guidelines are constantly reviewed and updates are built when new information becomes available.

Level 1 Evidence is collected from PUBMED and we include:
Meta-analysis, systematic reviews, randomized controlled trials, and evidence-based practice guidelines.

Access the Graded Evidence System

Professor André Elewaut and Professor Johan Fevery
WGO is honored to have been able to enlist the expertise and assistance of Professors Elewaut and Fevery in the grading of evidence to support practice guidelines. Each citation is assessed in terms of the quality of an article and how relevant it is for the guideline topic in question. Articles are then scored by assigning one or several stars:

Grade Key
Key Development
Very Important
  Special Mention


Gastroenterology and hepatology journals scanned:
Rank/Impact Factor Journal
1 Gastroenterology
2 Hepatology
3 Gut
4 Journal of Hepatology
5 Nature Reviews Gastroenterology and Hepatology
6 American Journal of Gastroenterology
7 Seminars in Liver Disease
8 Clinical Gastroenterology and Hepatology
9 Endoscopy
10 Gastrointestinal Endoscopy
General medical journals scanned:
Rank/Impact Factor Journal  
1 New England Journal of Medicine
2 Lancet
3 JAMA-Journal of the American Medical Association
4 Annals of Internal Medicine
5 PLOS Medicine
6 BMJ - British Medical Journal
7 JAMA Internal Medicine
8 Canadian Medical Association Journal
9 BMC Medicine
10 Cochrane Database of Systematic Reviews

Graded Evidence is an iterative process - and for that reason need not be so concerned with searching both Medline, Embase, and Biosis for example. All top GI journals are covered by both Medline and Embase and in single one-off complex searches unique citations in one or the other are often due either to differences in database currency or differences in coverage of less important journals. In addition to cost issues, the generous republishing and copyright policies of the US National Library of Medicine (NLM) make Medline the preferred choice. The WGO Graded Evidence library is grateful to the NLM for making data available to clinicians and practitioners outside the US for free.

Search Strategies
Search strategies for each topic
are based on a combination of controlled access and free text terms. The strategies aim for 'precision rather than 'sensitivity.' Highly sensitive search strategies as for example used by the Cochrane Collaboration when collecting literature reviews produce many irrelevant records. The advantage is these strategies retrieve all records which are relevant to a topic. But the 'number needed to read' is large and thus time consuming. Busy gastroenterologists probably prefer very precise search strategies in top GI journals and thus make sure every major article is found. The WGO Graded Evidence works along the lines of PUBMED Medline 'Clinical queries' features. Precise searches only find relevant information. Indexing errors may still be responsible for irrelevant or duplicate records. Case studies and animal studies are not usually included.

Graded Evidence records link directly to Pubmed-Medline and from here the searcher can follow the various link options to find similar records or an indication of how to find full text.

Please consult WGO's Ask a Librarian (AAL) system to request specific help with search strategies or your individual search requirements. The AAL service is free to all gastroenterologists in 'developing nations.' Let us know how we can improve our Graded Evidence system by sending us any evidence we may not have included in our listings for that topic.

Please consult WGO's Virtual Library System for more detailed search strategies and your individual search requirements. The Virtual Library functionality is based on PubMed’s feature of allowing a search strategy to be captured as a web address.