Systematic Reviews
Title Systematic Searching
What is grey literature?
Definitions of grey literature vary, but it is generally accepted to mean any literature that is not formally published in conventional and established formats.
Some examples of grey literature include:
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Uses for Grey Literature
It will depend on the purpose and scope of your review whether or not to include grey literature in your search, however, there are a number of reasons why it may be important to include in your review:
- Grey literature can provide further sources of evidence for your review;
- It can provide a more rounded view of your field of research with access to different perspectives;
- It can help balance publication bias e.g. often negative and neutral research results are not published by conventional means;
- It can be a source of raw data; and
- It can provide more currency to your review through access to the most up-to-date and pre-publication material
Challenges of using grey literature
Searching for grey literature can be a time-consuming process, as you may need to search in many different places to find relevant material which may be difficult to locate and access. This makes searching grey literature systematically a challenging process.
Depending on your topic and available time, you may decide to search all or a limited range of grey literature.
You will also have to carefully assess the quality and validity of the information when searching this type of material.
How to search for grey literature
Methods of searching for grey literature may include:
- Specific Grey literature database searches e.g. King's Fund, Scopus, Ethos, preprint servers etc.
- Hand-searching
- Targeted searching, e.g. relevant organisations
- Correspondence with field experts
- Google (the very last place to search. You should plan how many results you are willing to look at, e.g. top 100 only.
Using grey literature in your review
As part of your overall search methodology or planning, you may wish to clearly articulate how you intend to approach searching for grey literature. You may wish to incorporate this into your search plan. Your grey literature search plan should aim to include how and where you intend to search and the rational behind this.
You may also need to record grey literature searching and results in a different way, and separately from other database searching.
Searching multiple source formats and platforms or employing alternative methods of data collection (e.g. correspondence with experts) means it will not be possible to replicate the same kind of search strategy you would use for mainstream sources.
You will also need to consider how you will record the information you find, as not all grey literature sources may be able to be integrated with referencing software.
| Database / Web Site | Date | Search Terms | URL | Results |
| 3ie Database of Impact Evaluations | 09/05/11 | Melaria |
http://www.3ieimpact.org/ page.php?pg=search_impact &keyword=malaria+&x=13&y=4 |
25 |
| African Index Medicus | 05/05/11 | Search on : "MALARIA" or "MALARIAE" or "PLASMODIUM" or "MOSQUITO" or "MOSQUITOES" [Key Word] and "BEDNETS" or "NET" or "NETTING" or "CURTAINS" or "BEDDING" [Key Word] | http://indexmedicus.afro.who.int/ | 25 |
| 26/05/11 |
STRATEGY 1: allintitle: malaria AND (bednet OR bednets OR net OR nets OR curtain OR curtains OR netting OR ITNs) AND (own OR ownership OR possession OR use OR usage OR uses OR cost OR afford OR delivery OR subsidy OR subsidize OR purchase OR price OR utilize OR utilization OR voucher OR vouchers OR campaign OR program OR programs OR distribution) STRATEGY 2: Search: allintitle: malaria AND (bednet OR bednets OR net OR nets OR curtain OR curtains OR netting OR ITNs) AND (random OR randomly OR randomized OR controlled OR trial OR intervention OR clinical OR "pre‐post test" OR "time interrupted" OR "before and after" OR RCT OR CBA OR CCT OR ITS) |
scholar.google.com | 98 |
This table is an extract from Appendix 2 of a Cochrane Review on Strategies to increase the ownership and use of insecticide-treated benders to prevent malaria.
Sources of grey literature
EThOS
CURRENTLY UNAVAILABLE
The UK’s national thesis service which aims to maximise the visibility and availability of the UK’s doctoral research theses.
medRxiv
medRxiv is a preprint server for the health sciences. Preprint servers, house preprints (research that is yet to be published) and are classified by subject.
PsyArXiv
PsyArXiv is a preprint server for the psychological sciences. Preprint servers, house preprints (research that is yet to be published) and are classified by subject.
bioRxiv
bioRxiv is a preprint server for the biological sciences. Preprint servers, house preprints (research that is yet to be published) and are classified by subject.
CADTH Grey Matters
A Canadian tool for finding health-related grey literature that are not published commercially and which may be inaccessible via bibliographic databases.
Prospero
An international database of prospectively registered systematic reviews in health and social care, welfare, public health, education, crime, justice, and international development, where there is a health related outcome.
The King's Fund
An independent charitable organisation working to improve health and care in England with a huge archive of grey literature
Can be used at the very end of your grey literature search. You should complete all your searching (for peer reviewed journal articles, and all grey literature) first, and the Google search is to find anything that the more systematic searching did not.
Plan to only look at a certain number of results (e.g. top 100) from your Google search, because there could be thousands.
Your Google search should end your grey literature search.