Introduction

Grey literature "refers to print or electronic literature that is produced by government, academia, business and industry, and is not controlled by commercial publishers" (ICGL Luxembourg definition, 1997. Expanded in New York, 2004).

Examples include conference papers, clinical trials, reports, theses, fact sheets, research in progress, government publications, statistics, and more. Sources of grey literature include:

• Experts in the field
• Clinical Trial Registers
• Organisation/stakeholder websites
• University websites and institutional repositories
• Advanced internet searching

Get a complete, detailed view of current research

• Important for systematic reviews and other rigorous approaches to evidence synthesis
• Source data, statistics and very recent research results
• Find more detailed information than journal literature - no publisher-enforced limitation on length

Publication bias

• Publication lag - results of studies may appear a year or more before they appear in peer-reviewed publications
• Positive result bias - study results that show a negative or no effect are published in scholarly journals less often than those that show a positive effect

Credibility and bias

It is important to identify whether the information contained in grey literature is credible - "worthy of belief or confidence, trustworthy, reliable" (Oxford English Dictionary).

Be aware of private research organisations, drug companies, think tanks, etc. as they have their own commercial, political or social interests and biases.