Grey literature includes a wealth of information such as conference materials, datasets, discussion forums, dissertations and theses, government and local government papers, interviews, market reports, newsletters, pamphlets, policy statements, pre-print articles, research reports and survey results.
Internet searching can be really useful because results are often very current and bypass the peer review/publishing process. This means that it can be useful when looking at new or emerging areas of research. However, as it's not peer reviewed it can be of variable quality. You will need to assess the quality of this information yourself and decide if it appropriate to include in your work. The tutorial below will help you to do this.
The SIFT guide is a useful introduction to the principles of searching the internet to find high quality information.
Mike Caulfield. CC BY 4.0, via Hapgood.US
STOP – What is the source of the information? What is the reputation of the information and the source?
INVESTIGATE – What are you reading? Who produced the information? Knowing the expertise and agenda of the source is crucial to understanding the significance and trustworthiness of the information.
FIND BETTER COVERAGE – look for trusted sources to verify the information – “go out and find the best source you can on this topic, or, just as importantly, to scan multiple sources and see what the expert consensus seems to be”
TRACE – try and find the original context for the information you are looking at. Viewing it in it’s original context will help you get a sense of how accurately the information it being presented.