Although technological advances now allow us to ask our smartphone or nearby smart speaker to scour the Internet in search of the most unimportant piece of trivia, effectively searching scholarly literature databases remains a high-touch, iterative process that is learned and refined over time. For the discussion presented here, searching the literature refers to searching electronic databases of published works relevant to a researcher's field of interest. Although many helpful tips, guides, and literature-searching tutorials have been developed in recent years, these are often framed within the context of evidence-based practice (EBP), where the goal of the literature search is to locate evidence on the effectiveness of certain interventions in a defined population (Robb & Shellenbarger, 2014; Whalen & Zentz, 2015). Literature searches done preparatory to research differ from those done to answer an EBP question in terms of purpose, scope, inclusive dates, type of literature sought, and type of database used.
Literature searches done in preparation for research are necessarily broader than those done for the purposes of EBP. These broader searches do not constrain the search to intervention studies, or even to quantitative studies. While a researcher may hold great interest in the findings from applicable intervention studies, nonexperimental studies, evaluation reports, literature syntheses, editorials, and non-journal publications may be equally important to the researcher. This diverse array of scholarship can help highlight the importance of the topic of interest, document methodological approaches employed in studying the topic thus far, and identify lessons learned in previous research so these can be avoided in the future.
Similarly, although many literature searches conducted in support of EBP questions or projects may be restricted to articles published in the prior 5 to 10 years (thought to promote relevance), literature searches preparatory to research often seek to track the development of a concept or research topic over time, requiring that both recent and historical database entries be considered. Perhaps given the frequency with which articles on the topic are published at the present time, nursing faculty are often surprised to learn that predicting students' performance on the nursing licensure examination has been of interest to researchers for at least the past 50 years (Ruiz, 1967). This fact may have little relevance to faculty searching the literature on predictors of licensure examination success as they prepare to review their admissions and progression policies. It should be of more obvious importance to researchers considering conducting a similar study today, using much the same approach and methods used more than 50 years ago.
Finally, although it may be acceptable to limit searches of clinical topics to the largest and most well-known of the databases, such as MEDLINE® (U.S. National Library of Medicine, 2019) for the biomedical literature and CINAHL® (EBSCO Industries, Inc., 2019) for nursing-focused publications, nursing education researchers may need to search these and other additional databases such as ERIC™ (U.S. Department of Education, Institute of Education Sciences, 2019), which focuses on educational literature, and PsycINFO® (American Psychological Association, 2019), which focuses on the psychological and behavioral science literature. The need to search numerous databases covering fields that are both directly and indirectly related to nursing highlights the broad scope and increased depth required for the research literature search, compared with a focused search for evidence on a specific subject.
A nonexhaustive list of strategies to enhance the literature search process is outlined below. Unless otherwise noted, example nomenclature, terminology, or technical examples are based on MEDLINE and CINAHL. Field names appear enclosed in brackets and search strings appear in single quotes; the quote signs are not used when inputting the search string.
Understand the Nature and Contents of the Databases Being Searched
MEDLINE is a bibliographic database of over 25 million medical and biomedical research records, expanding by nearly 1 million new records each year, curated by the National Library of Medicine®. Providing coverage back to 1966, nearly all the records in MEDLINE are from peer-reviewed journals (U.S. National Library of Medicine, 2019). Although access to MEDLINE is available through a range of library database vendors, the National Library of Medicine has made access to MEDLINE free through its popular PubMed® portal ( https://pubmed.gov), which includes coverage of additional resources not indexed in MEDLINE. Access to CINAHL is provided on a subscription basis by EBSCO Industries, Inc. CINAHL provides indexing for more than 4,000 nursing and allied health journals, as well as numerous other document types including dissertations, book chapters, books, and conference proceedings, some dating back as far as 1937 (EBSCO Industries, Inc., 2019). It should be noted that because many journals are indexed by more than one database, finding duplicate listings in a multi-database search result lists is not uncommon. Each literature database provides a list of the publications it indexes, accessible from the database's publicly facing Web page and also within the database search interface.
Understand and Use Search Fields and Controlled Vocabularies
Literature databases are not unlike other databases in that the basic building block is a field that contains searchable information about the indexed item, which can be a journal article, book chapter, or conference abstract. Literature databases commonly allow searching by author name [AU] and institutional affiliation [AD], among numerous other fields. Perhaps the most important of the searchable fields are the controlled vocabulary fields used by the literature database. For MEDLINE, the controlled vocabulary is contained in the more than 25,000 item Medical Subject Headings (MeSH) taxonomy of subjects/topics. MeSH terms are hierarchically organized subject terms assigned by trained indexers. CINAHL indexes items using its own subject heading structure, which is based on MeSH headings. Each of these lists of subject headings is updated annually to reflect new terms that have entered use in the published literature.
Because subject headings are assigned to an indexed item by trained indexers, subject heading searches can be used to find articles that address similar topics, independent of the terminology or keywords supplied by authors or journals. For example, the MeSH heading ‘Education, Nursing’ is a general subject heading with several more specific subheadings for each of the major types of nursing education programs. Searching on only the heading ‘Education, Nursing, Associate’ will return only items indexed as such; searching under the broader term will return results indexed for the corresponding baccalaureate, graduate, or continuing education subheadings. Subject headings can also be cross-referenced to other synonymous or closely related terms to expand the number of items returned in a search. For example, in the ERIC database, the term remediation is a synonym for the preferred term, remedial instruction, which along with other related terms can be searched to provide a more complete list of results.
Understand and Use Boolean Operators, Parentheses, and Truncation and Wildcard Symbols
Boolean search logic consists of just three words: AND, OR, and NOT. Use of the AND operator means that all results will contain only items that contain all the terms searched. So, the search string ‘nursing AND education AND simulation’ will return items that contain all three terms. Adding parentheses to the search string allows even more specificity by allowing some, but not all, search terms to be combined with one another or to include items indexed using synonymous or alternative terms. For example, the search string ‘nursing education AND (quiz OR test OR exam) and guidelines’ will return results that include the terms nursing education and guidelines, along with any of the test-related terms in parentheses. Although the same search result list could be assembled from separate searches for each type of test, by including all the relevant terms inside parentheses using the Boolean OR operator, a single de-duplicated results list is produced using just one search.
Finally, truncation and wildcard symbols—and especially the asterisk—are perhaps among the most underappreciated tools in the literature search. The asterisk symbol (*) is used to search words or terms that have variable endings but that should be simultaneously searched. For example, searching using the string ‘nursing AND education AND competen*’ would return results that included the terms nursing and education, along with any recognized complete word that begins with ‘competen’ such as competent, competency, and competencies. This is a very useful tool for efficiently locating items that use a word form or the plural of the word that falls outside the exact form specified in the search string. However, misplacing a Boolean operator, parenthesis, or wildcard symbol can derail a search, so attention to detail is key.
Understand the Limitations of the Search Interface Through Which the Literature Search Is Conducted
Academic libraries are increasingly providing users with access to unified search tools through which multiple databases can be searched at once. These tools, while convenient, may not provide all the functionality and reliability available by searching databases individually. Because different databases handle Boolean operators, wildcard symbols, and subject headings differently, results lists from these searches should be checked against the results list obtained by using the same search string in the primary database. In general, MEDLINE and CINAHL can be simultaneously searched with few or no limitations. Other databases such as ERIC and PsycINFO may handle search commands differently and, thus, results lists may differ depending on the search interface and associated options selected by the user.
Finally, readers would be well-served in checking with their library staff about the consequences of checking the full text-only limiter box when searching any database. Checking this box may limit the results list to only those full-text sources housed within the database being searched and not to the entirety of a library's full-text holdings. For example, if a CINAHL search is restricted to full-text items only, the results list will omit items that are indexed in CINAHL but are not available in full-text form directly from CINAHL. The full text of these items is often available through a subscription the library holds with a different information vendor or with the publisher directly. To demonstrate, although CINAHL indexes articles published in the Journal of Nursing Education, direct full-text access within CINAHL is available only through part of 2011. Thus, when I search CINAHL using the string ‘JN Journal of Nursing Education’ with the full-text limiter selected, 3,656 results are returned and the most recent one is from 2011; with the full-text limiter unselected, 4,821 results are returned, including items published up through the most recent issue of the journal. Because most academic libraries have integrated some type of full-text finder tool within their search interfaces to address this issue, there are few reasons to limit searches of any database to full-text only.
Conducting a thorough and accurate search of the literature is a critical step in the planning phase of a research project. Incomplete or inaccurate literature searches can result in incomplete or inaccurate depictions of what is known on a given topic, which can result in a litany of negative downstream consequences for the study itself and for the researchers conducting it. Researchers can avoid these issues by learning how the literature relevant to their topical area is indexed by various database providers, the tools for expanding and limiting search results, and how to use a database's controlled vocabulary to conduct literature searches. Academic librarians can provide expert assistance and guidance in the literature searching process, but the rigor and completeness of the literature review remains the sole responsibility of study investigators.
Please send feedback, comments, and suggestions for future Methodology Corner topics to Darrell Spurlock, Jr., PhD, RN, NEA-BC, ANEF, at
- American Psychological Association. (2019). PsycINFO®. Retrieved from https://www.apa.org/pubs/databases/psycinfo/index
- EBSCO Industries, Inc. (2019). CINAHL® databases. Retrieved from https://www.ebscohost.com/nursing/products/cinahl-databases
- Robb, M. & Shellenbarger, T. (2014). Strategies for searching and managing evidence-based practice resources. The Journal of Continuing Education in Nursing, 45, 461–466. https://doi.org/10.3928/00220124-20140916-01 doi:10.3928/00220124-20140916-01 [CrossRef]
- Ruiz, R.A. (1967). Intellectual factors, biographical information, and personality variables as related to performance on the professional nurse licensure examination. Nursing Research, 16, 74–78. doi:10.1097/00006199-196701610-00015 [CrossRef]
- U.S. Department of Education, Institute for Education Sciences. (2019). ERIC help and FAQ. Retrieved from https://eric.ed.gov/?faq
- U.S. National Library of Medicine. (2019). MeSH browser. Retrieved from https://meshb.nlm.nih.gov/search
- Whalen, K.J. & Zentz, S.E. (2015). Teaching systematic searching in a baccalaureate nursing research course. Worldviews on Evidence-Based Nursing, 12, 246–248. https://doi.org/10.1111/wvn.12090 doi:10.1111/wvn.12090 [CrossRef]