Examining the Strength of the Evidence

Evidence-based practice guidelines are developed through the synthesis of the literature on the clinical problem. The purpose of the literature review designed to examine the strength of the evidence is to identify all studies that provide evidence of a particular intervention, to critically appraise the quality of each study, and to synthesize all of the studies providing evidence of the effectiveness of a particular intervention. It is also important to locate and include previous evidence-based papers that have examined the evidence of a particular intervention, because the conclusions of the authors of such papers are highly relevant. Literature syntheses related to promoting evidence-based nursing practice are described in Chapter 19.

Developing a Qualitative Research Proposal

In qualitative research, the purpose and timing of the literature review depend on the type of study to be conducted (see Chapter 12). Some phenomenologists believe that the literature should not be reviewed until after the data have been collected and analyzed, so that the literature does not interfere with the researcher’s ability to suspend what is known and to approach the topic with openness (Munhall, 2012). In the development of a grounded theory study, a minimal review of relevant studies provides the beginning point of the inquiry, but this review is only a means of making the researcher aware of what studies have been conducted. This information, however, is not used to direct the collection of data or interpretation of the findings in a grounded theory study. During the data analysis stage, a core variable is identified and the researcher theoretically samples the literature for extant theories that may assist in explaining and extending the emerging theory (Munhall, 2012). In historical research, the initial review of the literature helps the researcher define the study questions and make decisions about relevant sources. The data collection is actually an intense review of published and unpublished documents that the researcher has found.

The purposes of reviewing the literature for ethnographic studies and for exploratory descriptive qualitative research are more similar to that for quantitative research. The researcher develops a general understanding of the concepts to be examined in relation to the selected culture or topic. The literature review also provides a background for conducting the study and interpreting the findings. Chapter 12 describes in more detail the role of the literature review in qualitative research.

Developing a Quantitative Study

The review of literature in quantitative research directs the development and implementation of a study. The focus of the major literature review at the beginning of the research process is to identify a gap in what is known. The study is designed to add knowledge in the area of the identified gap. For example, an intervention to prevent hospital-acquired infections related to intravenous infusions has been shown to reduce the incidence of these infections among postoperative patients who have no history of diabetes mellitus. After a thorough review of the literature, the researcher identifies a specific gap in knowledge. What is not known is whether this intervention will be equally effective for postoperative patients who have diabetes. After the data have been analyzed and the findings described, the researcher will return to the literature in the generalization phase of the research report to integrate knowledge from the literature with new knowledge obtained from the study. The purposes of the literature review are similar for the different types of quantitative studies (descriptive, correlational, quasi-experimental, and experimental).

Table 6-1 describes the role of the literature throughout the development and implementation of the study. The types of sources needed and how you will search the literature will vary throughout the study. The introduction section uses relevant sources to summarize the background and significance of the research problem. The review of the literature section includes both theoretical and empirical sources that document the current knowledge of the problem. The researcher develops the framework section from the theoretical literature and sometimes from empirical literature. If little theoretical literature is found, the researcher may need to develop a tentative theory to guide the study from the findings of previous research studies (see Chapter 7 for more information). The methods section describes the design, sample, measurement methods, treatment, and data collection process of the planned study and is based on previous research. Thus, previous studies may be cited in the methods section. In the results section, sources are included to document the different types of statistical analyses conducted and the computer software to conduct these analyses. The discussion section of the research report begins with what the results mean in light of the results of previous studies. Conclusions are drawn that are a synthesis of the cited findings from previous research and those from the present study.

How Long Will the Review of the Literature Take?

The time required to review the literature is influenced by the problem studied, sources available, and goals of the reviewer. The literature review for a topic that is focused and somewhat narrow may require less time than one for a topic that is broad. The difficulty you experience identifying and locating sources and the number of sources to be located also influence the time involved, as does the intensity of effort. Only through experience does one become knowledgeable about the time needed for a literature review.

The novice reviewer requires more time to find the relevant literature than an experienced searcher, and the novice frequently underestimates the time needed for the review. An experienced librarian who works closely with nursing graduate students on a variety of course assignments recommends that the reviewer estimate the time required on the basis of the number of sources required and the reviewer’s familiarity with the library’s databases. The reviewer knows he or she needs at least 30 sources and that finding these sources may require 10 hours of searching. The reviewer estimates that it will take another 20 hours to read and synthesize the sources. The reviewer estimates that the review will require 30 hours. The reviewer should then multiply that number by four, making the estimated time required for the review 120 hours. This longer estimate is often more realistic. As searching skills are refined, the need to use this expanded estimate reduces. Often, the literature review is limited by the time that the reviewer can commit to the assignment. The conclusion related to the time issue is to start as early as possible and stay focused on the purpose of the review.

How Many Sources Do I Need to Review?

Students repeatedly ask, “How many articles should I have? How far back in years should I look to find relevant information?” The answer to both those questions is an emphatic “It depends.” Course faculty for masters courses commonly require that you obtain full-text articles of all studies relevant to the variables in the proposed study that were published in the previous 10 years. The instructors often indicate, however, that the length of time may vary depending on the topic and the presence of classic studies. Doctoral students are expected to conduct a more extensive review for course papers. If you are writing a research proposal for a thesis or dissertation, the literature required will be extensive. You need to locate the key papers in the field of interest. After doing some initial searches, discuss what you find with your instructor, thesis chair, or dissertation chair, who will be able to help you determine a reasonable publication period for you to use in your review.

Am I Expected to Read Every Word of the Available Sources?

The answer is “No.” If researchers attempted to read every word of every source that is somewhat related to a selected problem, they would be well read but would probably never complete their searches or move on to developing study proposals. Some individuals, even after a thorough literature review, continue to believe that they do not know enough about their area of interest, so they persist in their review; however, this activity ultimately becomes an excuse for not progressing with their work. The opposite of this situation is the individual who wants to move rapidly through the review of literature to reach the conclusion or get to the part of the work that is more enjoyable or important.

With the availability of full-text online articles, the researcher can easily get “lost in the literature” and forget the focus of the review. Becoming a skilled reviewer of the literature involves finding a balance and learning to identify the most pertinent and relevant sources. On the other hand, you cannot critically appraise and synthesize what you have not read. Avoid being distracted by nonrelevant information provided by the author. Learn to read with a purpose and involve multiple senses in your reading. Try reading aloud a section that you have difficulty understanding. Are you having difficulty following an author’s presentation? Try writing an outline. Draw a diagram of key points. Audio record your thoughts on the content of an article. Listen to soothing music if you are tense or anxious. Listen to music with an upbeat tempo if you are tired and having trouble staying awake. Try reading in a quiet place outside or standing up with the copy of the article or your laptop on a counter or high table. Involving multiple senses while reading may help you stay awake and focused.

Searching the Literature

Before writing a literature review, you must first perform literature searches to identify sources relevant to your topic of interest. The literature review will help you narrow your topic and develop a feasible study (Hart, 2009). Whether you are a student, practicing nurse, or nurse researcher, your goal is to develop a search strategy designed to retrieve as much of the relevant literature as possible given the time and financial constraints of your project.

Libraries have become gateways to information or information resource centers, rather than storehouses of knowledge (Hart, 2009). High-quality libraries provide access to a large number of electronic databases that supply a broad scope of the literature available internationally, enabling library users not only to identify relevant sources quickly but also to read full-text versions of most of these sources immediately. When your library does not have the hard copy of a book or electronic access to a specific journal, the librarian can usually provide the book or an electronic copy of the article through interlibrary loan. All libraries, public, private, college, and university, have interlibrary loan capabilities. You may especially need to use interlibrary loan when sources relevant to your topic were published prior to the advent of electronic databases.

Consider consulting with an information professional, such as a subject specialist librarian, to develop a literature search approach (Booth, Colomb, & Williams, 2008; Tensen, 2010). Often these consultations can be performed via email or a web-based meeting, so that communication occurs at the convenience of both the researcher and the information professional. Many university libraries provide this consultation service whether or not the library user is affiliated with the university.

Develop a Search Plan

Before you begin searching the literature, you must consider exactly what information you are seeking. Expending time and effort in the early stage of a review to develop a search strategy is likely to save time and effort later (Hart, 2009). A written plan helps you to avoid duplication of effort, to return to a previously searched area with a different set of search terms or a different range of publication years. Your initial search should be based on the widest possible interpretation of your topic. This strategy enables you to envision the extent of the relevant literature. As you see the results of the initial searches and begin reading the material, you will refine your topic, and then you can narrow the focus of your searches.

As you search, add your selected search terms to your written search plan. As you search, add other terms that you discover from the references you locate. For each search, record (1) the name of the database, (2) the date, (3) search terms and searching strategy, (4) the number and types of articles found, and (5) an estimate of the proportion of the citations you retrieved that were relevant articles. Table 6-2 is an example of search history that you can use to record what and how you have searched the literature. Save the results of each search on your computer or external device. Some databases allow you to create an account and save your search history online (i.e., the record of what and how you searched).

Select Databases to Search

A database is computer data that have been collected and arranged to be searchable and automatically retrievable (Tensen, 2010). A bibliographical database is an “an electronic version of a bibliographic index” (p. 57) or compilation of citations. The database may consist of citations relevant to a specific discipline or may be a broad collection of citations from a variety of disciplines. Databases of periodical citations include the authors, title, journal, keywords, and usually an abstract of the article. Library databases contain titles and authors of hard copy books and documents, government reports, and reference books. Library databases also include a searchable list of the journals to which the library has a paper or electronic subscription. For example, your library may have received paper copies of a monthly journal in the mail until 2006. The hard copies of the issues were bound to create annual volumes of the journal. Since 2006, the library has subscribed to the electronic journal or a journal database that provides access to specific issues.

Bibliographical databases provided by the same vendor, such as those databases affiliated with EBSCO Publishing, allow you to search multiple databases simultaneously to save time. Usually the search engine will automatically delete duplicates of the same study. You can also change the order in which the results of the search are shown. For example, with the EBSCO Publishing databases, you can sort the citations by relevance, date descending (most current first), or date ascending (oldest to more recent).

Older sources of reference indexes are useful for sources published prior to the electronic databases. Card catalogs, abstract reviews, and indexes were the only ways to search for nursing references until 1955, when the Cumulative Index to Nursing and Allied Health Literature (CINAHL) began being published. Because the printed editions had red covers, you still may hear more experienced scholars fondly refer to “the Red Books.” The print version of CINAHL is still available in libraries, and you may find it useful when searching for citations published before 1982 or when bibliographic databases are not available (Tensen, 2010). In medicine, the Index Medicus (IM) was first published in 1879 and is the oldest health-related index. The Index Medicus includes some citations of nursing publications, with the number of nursing journals cited growing. CINAHL contains, however, a more extensive listing of nursing publications and uses more nursing terminology as subject headings. With the greater focus on interdisciplinary research, nurse researchers must also be consumers of the literature in the National Library of Medicine (MEDLINE), other government agencies, and professional organizations. Table 6-3 provides descriptions of commonly used bibliographical databases.

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