The guidance typically relates to reviews of intervention effectiveness so PICO — with its focus on intervention and comparator - is the dominant model used to structure literature search strategies [ 68 ]. PICOs — where the S denotes study design - is also commonly used in effectiveness reviews [ 6 , 68 ]. As the NICE handbook notes, alternative models to structure literature search strategies have been developed and tested. The NICE handbook also suggests the use of multi-stranded approaches to developing literature search strategies [ 4 ].
Glanville developed this idea in a study by Whitting et al. Hausner et al. The conceptual approach, advocated by and explained in the guidance documents, relies on the expertise of the literature searcher to identify key search terms and then develop key terms to include synonyms and controlled syntax. Hausner and colleagues set out the objective approach [ 73 ] and describe what may be done to validate it [ 74 ].
The guidance documents offer direction on the use of limits within a literature search. Limits can be used to focus literature searching to specific study designs or by other markers such as by date which limits the number of studies returned by a literature search.
The use of limits should be described and the implications explored [ 34 ] since limiting literature searching can introduce bias explored above. Craven et al. Table 2 summarises the process of literature searching as reported in each guidance document. Three documents reported specific guidance on where to search, in each case specific to the type of review their guidance informed, and as a minimum requirement [ 4 , 9 , 11 ]. Seven of the key guidance documents suggest that the selection of bibliographic databases depends on the topic of review [ 2 , 3 , 4 , 6 , 7 , 8 , 10 ], with two documents noting the absence of an agreed standard on what constitutes an acceptable number of databases searched [ 2 , 6 ].
The documents provide guidance of selecting bibliographic databases, in some cases stating acceptable minima i. Studies have explored the value in searching specific bibliographic databases, with Wright et al.
The host of the database e. The average number of bibliographic database searched in systematic reviews has risen in the period — from 1 to 4 [ 80 ] but there remains as attested to by the guidance no consensus on what constitutes an acceptable number of databases searched [ 48 ]. 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.
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Fehrmann P, Thomas J. Comprehensive computer searches and reporting in systematic reviews. Research Synthesis Methods. Searching for qualitative research for inclusion in systematic reviews: a structured methodological review. Systematic Reviews. The most important are formulating the research questions and planning your search. Literature search is done to identify appropriate methodology, design of the study; population sampled and sampling methods, methods of measuring concepts and techniques of analysis.
It also helps in determining extraneous variables affecting the outcome and identifying faults or lacunae that could be avoided. Formulating a well-focused question is a critical step for facilitating good clinical research. Patient-oriented questions can involve the effect of therapy or disease or examine advantage versus disadvantage for a group of patients. For example, we want to evaluate the effect of a particular drug e.
It should either confirm, refute or add information to already done research work. One should also keep in mind the patient population under study and the resources available in a given set up. Also the entire research process should conform to the ethical principles of research. The patient or study population, intervention, comparison or control arm, primary outcome, timing of measurement of outcome PICOT is a well-known approach for framing a leading research question.
In this case scenario:. Patients P — What is the important group of patients? Intervention I — What is the important intervention? Comparison C — What is the important intervention of comparison? Outcome O — What is the effect of intervention? Time T — Time interval for measuring the outcome: Hourly for first 4 h then 4 hourly till 24 h post-procedure.
Multiple questions can be formulated from patient's problem and concern. A well-focused question should be chosen for research according to significance for patient interest and relevance to our knowledge.
Good research questions address the lacunae in available literature with an aim to impact the clinical practice in a constructive manner. There are limited outcome research and relevant resources, for example, electronic database system, database and hospital information system in India. Even when these factors are available, data about existing resources is not widely accessible.
Primary sources are the authentic publication of an expert's new evidence, conclusions and proposals case reports, clinical trials, etc and are usually published in a peer-reviewed journal. Preliminary reports, congress papers and preprints also constitute primary literature. Secondary sources are systematic review articles or meta-analyses where material derived from primary source literature are infererred and evaluated.
Tertiary literature consists of collections that compile information from primary or secondary literature eg. There are various methods of literature search that are used alone or in combination [ Table 1 ]. For past few decades, searching the local as well as national library for books, journals, etc. The various databases available for literature search include databases for original published articles in the journals [ Table 2 ] and evidence-based databases for integrated information available as systematic reviews and abstracts [ Table 3 ].
Links to the full-text material are included in citations from PubMed Central and publisher web sites. Education Resources Information Centre is a free online digital library of education research and information sponsored by the Institute of Education Sciences of the U. No one database can search all the medical literature. There is need to search several different databases.
When searching these databases, emphasis should be given to meta-analysis, systematic reviews randomised controlled trials and landmark studies. Time allocated to the search needs attention as exploring and selecting data are early steps in the research method and research conducted as part of academic assessment have narrow timeframes.
This results in the formulation of the inappropriate research question and increases the time to literature search. Type of search can be described in different forms according to the subject of interest.
It increases the chances of retrieving relevant information from a search. This will provide results based on any of the words specified; hence, they are the cornerstone of an effective search. Spellings should also be taken into account, i. Most databases use controlled word-stock to establish common search terms or keywords. Some of these alternative keywords can be looked from database thesaurus. It is important to keep a note of keywords and methods used in exploring the literature as these will need to be described later in the design of search process.
For example, if the search keyword is heart attack, this term will match with MeSH transcription table heading and then explode into various subheadings. This helps to construct the search by adding and selecting MeSH subheadings and families of MeSH by use of hyperlinks. We can set limits to a clinical trial for retrieving higher level of evidence i. This PubMed feature searches for similar citations using an intricate algorithm that scans titles, abstracts and MeSH terms.
This will provide pages with only the words typed in the phrase, in that exact order and with no words in between them.
Filters can also be used to refine the search, for example, article types, text availability, language, age, sex and journal categories. Overall, the recommendations for methodology of literature search can be as below Creswell [ 19 ].
Identify keywords and use them to search articles from library and internet resources as described above. 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:. Overlooking the importance of using the right keywords and phrases relevant to the topic means that you could miss important information due to a weak search query.
Many researchers tend to do a literature search taking into account published literature: journals and books. However, there are other sources that are invaluable, but often overlooked. Look into conference proceedings, ongoing research at university labs mentioned on university websites , online discussion forums, databases of high-quality pre-print material, and postdoctoral theses.
Examples of non-obvious sources for topic-specific literature:.
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