Searching the literature for research or professional purposes generally starts with established evidence-based sources such as textbooks, reference sources, guidelines, bibliographic databases and peer-reviewed journal articles. This article outlines the other resources available to you after you have completed your initial search and are seeking to broaden its scope. In this article, we describe a set of freely available search tools that will expand your search of the literature to find other published formats such as preprints and reports.
This approach has its dangers. You may encounter journal articles from predatory or junk journals and publications that have not been subject to peer review. This requires you to exercise critical judgement of the material. We point you to tools that will guide you through a critical evaluation.
Repositories
Repositories are essentially large databases of published and sometimes unpublished material. They are organised in two ways:
An example of a relevant institutional repository is amber—the Ambulance Research Repository (https://amber.openrepository.com). It contains publications by staff and researchers working in NHS ambulance services in England from 2006 to date, and is a unique record of publications about paramedicine. It contains records of publications not included in the major bibliographic databases mentioned in the introduction to this article. A search of amber will inform any research endeavour in the area of ambulance services and related topics. An example of a subject repository in biomedical and life sciences would be European PubMed Central (https://europepmc.org)
A number of search tools sift through multiple repositories to save you the trouble of searching them individually. Core (COnnecting REpositories) (https://core.ac.uk) is a search tool provided by the Jisc and the Open University in the UK that has a global reach. BASE (Bielefeld Academic Search Engine) in Germany (https://www.base-search.net) searches repositories and other sources with a similar global reach.
Academic search engines
Academic search engines (ASEs) search for scholarly content on the web. The most well-known is of course Google Scholar (https://scholar.google.com). However, there are others search engines including Microsoft Academic Search (https://academic.microsoft.com) and ScienceOpen (https://www.scienceopen.com). ASEs are characterised by their size. Google Scholar is estimated to contain over 389 million records (Gusenbauer, 2019); Microsoft Academic Search over 200 million records; and ScienceOpen 64 million records. All three include features such as personal profiles linked to your publications and citations. While Google Scholar has a spare search interface, both ScienceOpen and Microsoft Academic are feature-rich, allowing better opportunities to refine your search. Microsoft Academic is distinctive in using Microsoft's artificial intelligence (AI) technology, which goes beyond just keyword searching. Whichever ASE you choose to use—and you may use more than one—the point here is that each one reaches deep into the web to find material that you would not find in traditional bibliographic databases such as Medline and CINAHL.
Grey literature
Grey literature is made up of the reports and documents published by governments and their agencies, business and industry, and academia, that are not published by commercial publishers. In an organisation as complex as the NHS, with its many trusts and agencies, this is a particularly rich pool of information to search in. Health Education England supports its own grey literature service, the National Grey Literature Collection (http://allcatsrgrey.org.uk/wp). The National Institute for Health and Care Excellence (NICE) also provides NHS Evidence Search—the ‘Google’ of the NHS (https://www.evidence.nhs.uk) to enable access to the selected quality sources on healthcare and public health. For a broader perspective, WorldCat's OIAster database searches open-source material from around the world (https://oaister.worldcat.org).
Theses
Theses completed in UK universities are deposited with the British Library. To make better use of this rich resource, the British Library publishes EThOS e-theses online service (https://ethos.bl.uk). EThOS allows you to search over 500 000 theses, many of which are available in full text for download. The service is free; however, registration is required. In addition to EThOS, there is a website dedicated to PhDs in the area of paramedcine, ParamedicPhd (https://www.paramedicphd.com), which has worldwide coverage.
Preprints
A preprint is a version of a research manuscript published before peer review. Typically, these are published electronically and made publicly available on large databases or preprint servers. Publishing a preprint aims to speed up the process of disseminating research, avoiding the delays caused by the publication process. Publishing research as a preprint allows you to generate a conversation around your research and gain feedback from others. Authors would normally seek to publish their research in a peer-reviewed journal at a later date. Preprints have become more important as a source of information during the COVID-19 pandemic, as the need for speed in the dissemination of research has outpaced the traditional publishing process. However, reputable preprint servers urge caution when using preprints. This warning comes from the home page of medrxiv:
‘Caution: Preprints are preliminary reports of work that have not been certified by peer review. They should not be relied on to guide clinical practice or health-related behavior and should not be reported in news media as established information.’
The preprint servers most relevant to health are medRxiv (http://medrxiv.org) and bioRxiv (http://biorxiv.org). The search interface for both medRxiv and bioRxiv are relatively unsophisticated. You can use medrxivr (https://mcguinlu.shinyapps.io/medrxivr), a customised search app that adds a number of helpful features to improve your search. You also have the option of using Google Advanced Search (https://www.google.co.uk/advanced_search), which allows you to search specific websites.
Preprint search engines
The Open Science Foundation preprint search engine, OSF Preprints (https://osf.io/preprints) searches the preprint collections, OSF hosts and other preprint servers. The OSF website claims to search over 1 mllion preprints. The National Institutes for Health (NIH) have developed a pilot search project for preprints related to COVID19 (https://icite.od.nih.gov/covid19/search/) with the aim of speeding dissemination of research. Preprints are a fast-moving area of publishing and we may expect new preprint servers and related tools to be added to the ones described in this article.
Predatory journals
Predatory journals exploit a publishing model where the author pays to publish articles that are usually made freely available on the web. Predatory journals deceive authors by claiming to provide peer review and editorial services but, in fact, publishing anything submitted without scrutiny for a fee. Predatory journals use a number of strategies to disguise their true nature; however, with a few precautions and checks, it is possible to identify and avoid them. Use the Think, Check, Submit (https://thinkchecksubmit.org) website for advice on how to spot predatory journals and publishers. There is a guide taking a slightly different approach on the LKS ASE website (https://ambulance.libguides.com/predatoryjournals).
This matters because as you leave the safety of quality assurance provided by major bibliographic databases, and use tools like Google Scholar, predatory material will show up in your searches. In fact, one of the tell-tale signs of a predatory journal is the claim to be ‘Indexed by Google’.
Summary
Questions relating to specific clinical queries can generally be answered using established sources. You might consider broadening your search and using some of the tools in this article if:
It is important to be critical of the material you find—especially if it is from a source you don't know, hasn't gone through peer review or you suspect the journal may be predatory. If you need help and advice, consult your local NHS healthcare library where librarians can offer you expert guidance.