This is perhaps because thinking about the number of databases searched is the wrong question, researchers should be focused on which databases were searched and why, and which databases were not searched and why. The discussion should re-orientate to the differential value of sources but researchers need to think about how to report this in studies to allow findings to be generalised.
Search summaries document both yield and accuracy of searches, which could prospectively inform resource use and decisions to search or not to search specific databases in topic areas. The prospective use of such data presupposes, however, that past searches are a potential predictor of future search performance i. In offering a body of practice, this data would be of greater practicable use than current studies which are considered as little more than individual case studies [ 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 ].
When to database search is another question posed in the literature. Beyer et al. Cooper et al. Their case study compared the effectiveness of database searching versus a protocol using supplementary search methods and found that the latter identified more relevant studies for review than searching bibliographic databases [ 94 ].
Table 2 also summaries the process of literature searching which follows bibliographic database searching. As Table 2 sets out, guidance that supplementary literature search methods should be used in systematic reviews recurs across documents, but the order in which these methods are used, and the extent to which they are used, varies.
We noted inconsistency in the labelling of supplementary search methods between guidance documents. Rather than focus on the guidance on how to use the methods which has been summarised in a recent review [ 95 ] , we focus on the aim or purpose of supplementary search methods.
Only one document reported any guidance on determining when to use supplementary methods. This is in contrast to the guidance above on bibliographic database searching. The issue for supplementary search methods is similar in many ways to the issue of searching bibliographic databases: demonstrating value. The purpose and contribution of supplementary search methods in systematic reviews is increasingly acknowledged [ 37 , 61 , 62 , 96 , 97 , 98 , 99 , , ] but understanding the value of the search methods to identify studies and data is unclear.
In a recently published review, Cooper et al. This review also summarises the key guidance and empirical studies and seeks to address the question on when to use these search methods and when not to [ 95 ]. The guidance is limited in this regard and, as Table 2 demonstrates, offers conflicting advice on the order of searching, and the extent to which these search methods should be used in systematic reviews.
Five of the documents provided guidance on managing references, for example downloading, de-duplicating and managing the output of literature searches [ 2 , 4 , 6 , 8 , 10 ]. This guidance typically itemised available bibliographic management tools rather than offering guidance on how to use them specifically [ 2 , 4 , 6 , 8 ]. The CEE handbook provided guidance on importing data where no direct export option is available e.
Bramer et al. Coar et al. Managing references is a key administrative function in the process of review particularly for documenting searches in PRISMA guidance. Six documents provided guidance on reporting the process of literature searching with specific criteria to report [ 3 , 4 , 6 , 8 , 9 , 10 ]. There was consensus on reporting: the databases searched and the host searched by , the search strategies used, and any use of limits e.
Three guidance documents reported that the number of studies identified should be recorded [ 3 , 6 , 10 ]. The number of duplicates identified [ 10 ], the screening decisions [ 3 ], a comprehensive list of grey literature sources searched and full detail for other supplementary search methods [ 8 ], and an annotation of search terms tested but not used [ 4 ] were identified as unique items in four documents.
The Cochrane Handbook was the only guidance document to note that the full search strategies for each database should be included in the Additional file 1 of the review [ 9 ]. All guidance documents should ultimately deliver completed systematic reviews that fulfil the requirements of the PRISMA reporting guidelines [ ].
The guidance broadly requires the reporting of data that corresponds with the requirements of the PRISMA statement although documents typically ask for diverse and additional items [ ].
In , Sampson et al. Reporting of literature searching is a key area in systematic reviews since it sets out clearly what was done and how the conclusions of the review can be believed [ 52 , ].
Despite strong endorsement in the guidance documents, specifically supported in PRISMA guidance, and other related reporting standards too such as ENTREQ for qualitative evidence synthesis, STROBE for reviews of observational studies , authors still highlight the prevalence of poor standards of literature search reporting [ 31 , , , , , , , , , , ]. Atkinson et al. One area that is less well covered by the guidance, but nevertheless appears in this literature, is the quality appraisal or peer review of literature search strategies.
The PRESS checklist is the most prominent and it aims to develop evidence-based guidelines to peer review of electronic search strategies [ 5 , , ]. A corresponding guideline for documentation of supplementary search methods does not yet exist although this idea is currently being explored. How the reporting of the literature searching process corresponds to critical appraisal tools is an area for further research.
In the survey undertaken by Radar et al. The PRISMA statement offers a brief summary of what to report but little practical guidance on how to report it [ ]. Further research in the form of a study which undertakes a comparison between PRISMA and quality appraisal checklists for systematic reviews would seem to begin addressing the call, identified by Radar et al.
A potential limitation of this literature review is the focus on guidance produced in Europe the UK specifically and Australia. In brief, these nine guidance documents were selected as the most relevant health care guidance that inform UK systematic reviewing practice, given that the UK occupies a prominent position in the science of health information retrieval. We acknowledge the existence of other guidance documents, such as those from North America e. We comment further on this directly below.
What is not clear is the extent to which the guidance documents inter-relate or provide guidance uniquely. The Cochrane Handbook, first published in , is notably a key source of reference in guidance and systematic reviews beyond Cochrane reviews.
It is not clear to what extent broadening the sample of guidance handbooks to include North American handbooks, and guidance handbooks from other relevant countries too, would alter the findings of this literature review or develop further support for the process model. Since we cannot be clear, we raise this as a potential limitation of this literature review.
On our initial review of a sample of North American, and other, guidance documents before selecting the guidance documents considered in this review , however, we do not consider that the inclusion of these further handbooks would alter significantly the findings of this literature review.
A further limitation of this review was that the review of published studies is not a systematic review of the evidence for each key stage. It is possible that other relevant studies could help contribute to the exploration and development of the key stages identified in this review. This literature review would appear to demonstrate the existence of a shared model of the literature searching process in systematic reviews.
The findings reported above reveal eight key stages in the process of literature searching for systematic reviews. These key stages are consistently reported in the nine guidance documents which suggests consensus on the key stages of literature searching, and therefore the process of literature searching as a whole, in systematic reviews. In Table 2 , we demonstrate consensus regarding the application of literature search methods.
All guidance documents distinguish between primary and supplementary search methods. Bibliographic database searching is consistently the first method of literature searching referenced in each guidance document.
Whilst the guidance uniformly supports the use of supplementary search methods, there is little evidence for a consistent process with diverse guidance across documents. This may reflect differences in the core focus across each document, linked to differences in identifying effectiveness studies or qualitative studies, for instance. Eight of the nine guidance documents reported on the aims of literature searching. The shared understanding was that literature searching should be thorough and comprehensive in its aim and that this process should be reported transparently so that that it could be reproduced.
Defining the key stages in this review helps categorise the scholarship available, and it prioritises areas for development or further study. It is where search strategy structure is determined, search terms are chosen or discarded, and the resources to be searched are selected. Information specialists, librarians and researchers, are well placed to develop these and other areas within the key stages we identify.
This review calls for further research to determine the suitability of using the conventional approach. The publication dates of the guidance documents which underpin the conventional approach may raise questions as to whether the process which they each report remains valid for current systematic literature searching.
In addition, it may be useful to test whether it is desirable to use the same process model of literature searching for qualitative evidence synthesis as that for reviews of intervention effectiveness, which this literature review demonstrates is presently recommended best practice. Booth A. Unpacking your literature search toolbox: on search styles and tactics. Article Google Scholar. Petticrew M, Roberts H. Systematic reviews in the social sciences: a practical guide.
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Need help? Hire a literature search expert on Kolabtree. Choose from PhD-qualified researchers in over 2, subjects. A literature search involves searching and compiling all the literature books, journals, and more available on a specific topic.
It is carried out to identify knowledge gaps in a particular topic, which will then guide further research in that topic. It is also carried out to provide background in a study, support methodologies, provide context or comparisons for discussions, and more. One of the most important reasons to do a literature search is to have enough information to formulate a valid research question.
Literature can be compiled from a variety of sources. A primary source is published, peer-reviewed research available in the form of books and journals. Online databases provide access to published works available on the web. How can you make your literature search more effective? A literature search can be a daunting, tiring and time-consuming task. Since this activity forms the foundation for future research, it is essential for it to be absolutely comprehensive and accurate.
Errors in a literature search could mean loss of precious time, resources and energy. You could be carrying out research which has already been done before, using redundant, outdated methodologies, or designing experiments that have shown to be ineffective in the past. Starting off a literature review without an clear and focussed research question will mean that you will dig up a lot of literature not relevant to what you actually want.
So, develop a research question that is:. The first thing to do is to define your topic or research project; or, if you have been given a set question, make sure you understand it. Ask yourself what the key concepts are. Compile a list of keywords — and synonyms for them — and this will help you to develop a research strategy.
Search creatively. This may include: libraries, indexes and electronic databases, and the Internet. Use the library. Remember that every book and journal published in the UK is held at the British Library and you can do inter-library loans. Ask your library staff for assistance. Remember that journals are the best place to find the most recently published research. Newspapers and magazines are a good source for current topical issues, although they are not always very useful for in-depth analysis.
For example, if you are writing on a business-related topic you may find useful items in The Economist , Fortune and Harvard Business Review. For example, libraries contain books and journals but they also contain unpublished MA and PhD theses that may contain research relevant to your topic. Similarly, make sure you do speculative searches i. Conference papers. These collections are published on the Internet, in special editions of relevant journals and in one-off books.
National and local Government publications. These include reports, yearbooks, White and Green papers, policy documents, manuals and statistical surveys.
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