Nursing and Midwifery: Methodology

Searches you undertake in databases relevant to your topic might not be sufficient to find all the available evidence to answer your research question. You may need to undertake supplementary searches to help you identify key articles, people, concepts or other avenues for exploration from your original search. The amount of supplementary searching will vary depending on the discipline of your topic but can include: 

• Searching grey literature resources
• Searching clinical trials registers
• Citation searching
• Contact study authors or experts in your topic

What is Grey Literature? 

Grey literature refers to information and research outputs that are not formally published or distributed through traditional commercial or academic publishing channels. This means they are often produced by organisations such as governments, universities, hospitals, NGOs, think tanks, and professional associations but are not controlled by commercial publishers. The importance of Grey Literature varies by field. For example: Economics relies on working papers; Medicine depends heavily on Clinical Trial Registries. In other disciplines, grey literature may be less central, but still valuable. 

Examples include: 

• Technical reports 

• Conference abstracts and proceedings 

• Preprints 

• Patents 

• Government publications 

• Industry or NGO reports 

• Think tank papers 

• Working papers 

• Clinical trial registries 

• Dissertations and theses 

• Unpublished or ongoing studies 

Why Search Grey Literature? 

Searching Grey Literature is an essential part of a comprehensive and unbiased evidence synthesis. Here's why: 

• It contains original data not published elsewhere. Many conference presentations and reports never become journal articles, but still hold valuable evidence. 
• It reduces publication bias. Peer-reviewed journals often favour positive or statistically significant results. Grey literature can help uncover less-reported, non-significant findings that are just as important for decision-making. 
• It broadens perspectives. Grey Literature can include voices and research from underrepresented groups, regions, or organisations not well represented in traditional publishing. 

Including Grey Literature in your searching is recommended by major review bodies. Both Cochrane and Campbell Collaboration guidelines advocate for grey literature searches in systematic reviews. 

Strategies for Searching Grey Literature 

Because grey literature is so varied, there’s no one-size-fits-all search strategy. Use the following best practices: 

Go to the Source: 

Identify relevant organizations (NGOs, government bodies, think tanks, universities, professional associations) and search their websites directly. Create a target list of key organizations in your field before you begin searching.

Use Google Strategically
While Google searches can be overwhelming, they're valuable for grey literature when used with precision:

• Use Google Advanced Search to search specific sites (e.g., site:hse.ie) or limit results to domain types (.edu, .org, .gov)
• Try Google Scholar for academic grey literature like theses, preprints, and conference papers
• Use quotation marks for exact phrases and the minus operator (-) to exclude irrelevant terms

Explore Google's Search Help - Refine web searches for additional operators 

Learn from Others: Check systematic reviews and meta-analyses in your field to identify grey literature sources they used. Their reference lists are goldmines for discovering relevant organizations and repositories.

Talk to Experts: Subject experts, librarians, and practitioners often know which organizations or repositories publish relevant work. Reach out to colleagues and authors of key papers in your field.

Challenges with Grey Literature

Be Aware of Limitations:

• Discoverability: Not indexed in standard databases (PubMed, Scopus, Web of Science)
• Quality concerns: Variable quality and often lacks peer review
• Citation challenges: May be difficult to cite properly or access long-term
• Search limitations: Many websites lack advanced search options or clear organization

Practical Tips:

• Keep searches simple and flexible - complex search strings often fail on organizational websites
• Document everything: Save copies of documents and record access dates, as grey literature can disappear
• Use Internet Archive's Wayback Machine (https://web.archive.org/) when links no longer work
• Cast a wide net initially, then narrow down based on relevance and quality
• Plan extra time for evaluation, as screening grey literature often requires more interpretation than peer-reviewed sources

Documenting Grey Literature Searches 

Documentation is critical for transparency and reproducibility, though it can be more challenging than with database searches. 

Aim to record the following. Use a simple spreadsheet, Google Sheets or Excel,  to track these elements, a column for each element:

• Name of the source or website 

• URL 

• Date of search 

• Search terms used 

• Number of results 

• Any instructions or notes on how the search was conducted 

Tools and Tips 

• Reference Management Software such as Zotero can be used to capture and store Grey Literature (including metadata or web snapshots). 
• RIS file exports from citation managers can help integrate grey literature into screening tools (e.g. Covidence and Rayyan). 
•  Multiple searches may be needed on the same site using different search terms, due to limited functionality. 

Clinical trials registers are publicly accessible, online databases of planned, ongoing and completed clinical trials. They store detailed information about trial protocols, methodologies, and outcomes, ensuring transparency and accessibility for researchers, healthcare professionals, and the public.

As they include both published and unpublished studies, including trials with negative results, abandoned studies, and research that may never reach publication, searching these registers is essential for mitigating publication bias in systematic reviews. Many registers also contain trials that are years away from completion or publication, providing early insights into the research landscape.

When to Search
If you are undertaking a systematic review on the effect of an intervention, best practice and current guidelines (including PRISMA 2020) require you to search clinical trials registers. Many funding bodies now mandate this as part of grant applications.

Key Registers to Search
Primary International Registers

• ClinicalTrials.gov (US) - The largest register with over 400,000 studies from around the world
• WHO International Clinical Trials Registry Platform (ICTRP) - Meta-search portal accessing multiple international registers simultaneously
• EU Clinical Trials Register - European trials under EU legislation
• ISRCTN Registry - The UK's Clinical Study Register

Additional Registers

• Cochrane Central Register of Controlled Trials (CENTRAL) - Includes trials from multiple sources and databases
• Australian New Zealand Clinical Trials Registry (ANZCTR)

Search Strategy Tips
Terminology Considerations:

• Use broader, simpler search terms than in bibliographic databases
• Search both generic and brand names for drug interventions
• Include condition synonyms and relevant MeSH terms
• Account for different terminology and spelling variations across international registers

Key Fields to Search:

• Study title and brief summary/description
• Intervention names and comparators
• Condition/disease terms
• Primary and secondary outcomes
• Sponsor/organization information

Citation Searching

Due to the limitations of database searching and the reality of not being able to search every single database available, some studies may still be missed. Scholarly works have a past and a future, and these offer additional places to locate relevant studies for your systematic review. Citation searching is also known as ancestry searching, snow balling or pearl growing

There are two main ways citation searching can be conducted as part of the supplementary searching:

Backward Citation Searching

• Looking through reference lists of included studies
• Also examine reference lists of previously published reviews that are on the topic or similar to your evidence synthesis project
• Focus on the most recent and highly relevant included studies for efficiency

Forward Citation Searching

• Looking at the "cited by" lists for included studies
• Use tools like  Web of Science, Scopus or Google Scholar to identify papers that have cited your included studies
• Pay particular attention to recent citations that may have been published after your main database searches

Best Practices

• Prioritize key papers: Focus citation searching efforts on the most important/relevant included studies rather than all included studies
• Set time limits: Consider searching citations from studies published within the last 5-10 years, as older studies may yield diminishing returns
• Use multiple platforms: Different citation databases may capture different citing papers
• Document your process: Record which studies you citation searched, which databases/tools you used, and your date ranges

Tools for Citation Searching

• Web of Science: Comprehensive, provides citation reports and analytics
• Scopus: Strong coverage of recent literature, advanced citation tracking
• Subject-specific databases: Some disciplines have specialized citation tools
• Google Scholar: Free, broad coverage, good for forward citation searching
• Citation chaser: Automating the process of citation searching by using the Lens.org API

Integration with Your Review

When reporting the search methods, be sure to include:

• Details of the citation searching methodology
• Which studies were selected for citation searching and why
• How the resulting records from citation searches were screened
• Add any studies identified through citation searching to the identification section of the PRISMA 2020 flow diagram

Additional Resources

For comprehensive guidance on citation searching methodology, terminology, and reporting standards, consult:

The TARCIS Statement: Guidance on terminology, application, and reporting of citation searching. This evidence-based consensus statement provides 10 specific recommendations for conducting and reporting citation searching in systematic literature searches.

Cooper, C., Levay, P., Lorenc, T. et al. The TARCiS statement: guidance on terminology, application, and reporting of citation searching. BMJ 2024; 385 :e078384 https://doi.org/10.1136/bmj-2023-078384