A comprehensive systematic review takes literature and data from a broad spectrum of sources and uses it to answer a clearly-defined, specific question. But one source is making waves in research these days: grey literature. What is it? How do you use it? What are the benefits and challenges of using grey literature in systematic reviews?
What is grey literature?
Grey literature is a term coined in the 1970's. It describes literature and research documents that exist outside of "traditional" research materials.
Grey literature comes from all levels of government, business, and academics; however, the important thing to note is that it typically does not include documents controlled by commercial publishing. Many grey literature references are self-published.
As the internet grows, the realm of grey literature will evolve. Many experts want "grey literature" to be renamed "grey media" or "grey information" to include sources like social media, video, and other new media.
Why is grey literature important for research?
Grey literature is essential for researchers working on niche topics because it encompasses information that is not usually published by larger commercial or academic studies. Think of it this way: commercial organizations won't spend money publishing literature they don't think will be profitable. If there is a small audience, they are less likely to publish information because the primary goal of commercial literature is to make money.
Grey literature is also not bound by the same regulatory writing review processes of traditional types of literature. This means grey literature is published faster than classic literature, making it more current and timely for specific niche topics.
The benefits of grey literature
Gathering as much research material as possible is critical for a thorough review. This means mining traditional databases and normal academic channels as well as looking outside the box. In addition to preventing bias, grey literature helps give your research more context and could help you find brand-new information that traditional searches might have missed.
Using grey literature also ensures that your review is not susceptible to publication bias or selective outcome reporting. It’s a well-known fact in the systematic review community that outcomes and full studies showing benefit are more likely to be published over studies showing no benefit or harm, therefore, systematic reviews not searching for this kind of information may present a biased estimate of effect.
Grey literature challenges
Sounds excellent, right? Grey literature is produced quickly, provides essential context, and covers niche topics that traditional literature might miss. However, as great as grey literature might sound, it does present a few challenges for researchers:
- Since grey literature is usually self-published, it is not put through as stringent of an editing process as traditional literature. This means grey literature could have more inaccuracies, bias, or incomplete information.
- Pages on the internet do not always exist in perpetuity. Blogs, social media posts, or wikis are not always available if the host decides to take it down. Content found in databases and repositories have more longevity.
- Grey literature is not always indexed by traditional databases, which means it might be harder to find.
- Taking a systematic approach to grey literature is complicated. It is challenging to review grey literature on a large scale. Efficiency and reproducibility is an issue.
3 tips for using grey literature
If you are using grey literature in your systematic review, there are a few things you can do to :
1. Evaluate everything
It's important to be critical of all the information you find from alternate "grey" sources. This means evaluating everything from the author, publisher, purpose, content, objectivity of the source, and also the timeliness of the information. We strongly recommend giving grey literature the same level of scrutiny you would any other type of published material.
2. Get creative with searching
Grey literature is often more challenging to find than traditional research materials, so you may need to get creative. Google Scholar and Google Advanced Search are two useful grey literature search engines. You can also look to government agencies, company websites, OpenGrey, trial registries, and beyond. The realm of grey literature is expansive.
3. Ask for help
A qualified librarian is a valuable asset for any research team looking to add grey literature to their review.
Whether you currently use grey literature in your systematic reviews or not, chances are you will come across it at some point in the future. Knowing the benefits, challenges, and best practices for using grey literature will help keep your systematic reviews comprehensive, compliant, and accurate.
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