Evidence-based practice (EBP) is one of the hottest topics in health care. Yet many clinicians who provide direct patient care don’t know where the evidence in EBP comes from. The vast majority comes from research studies, although clinical expertise and patient values also are taken into account. Typically, the best evidence is developed through rigorous research studies and discovered while reviewing literature. Nurses involved in EBP may undertake literature reviews to find evidence or may seek to develop a formal written literature review.
Conducting a thorough literature review is a daunting task. For nurses who aren’t directly involved in academia or research, the types of reviews and the terminology used can be confusing. All nurses should be aware of and understand the origin of the evidence, the terminology used, and how the various types of literature reviews vary. This article distinguishes reviewing literature from reading literature reviews conducted by others, and describes the various types of literature reviews.
Defining literature review
When used as a noun, review means a retrospective survey. Anyone can review literature to search for evidence. In fact, reviewing literature is easier than ever, thanks to the Internet and the vast array of databases available. You can use a search engine, such as Google or Yahoo, or an electronic library, such as those found in academia and large healthcare organizations. In either case, you enter keywords or key phrases to find published information on a given topic.
Basic literature review
A basic literature review is conducted without a method or orderly process. Typically, those who review literature in this way use varying degrees of thoroughness, use limited rather than exhaustive means, and are selective based on their purpose. In other words, they tend to choose only those studies that support their personal topic-related bias. Such a literature review certainly will turn up evidence, but not necessarily the best evidence. (See Comparing formal literature reviews by clicking the PDF icon above.)
Written literature review
In contrast, a written literature review is an organized document or section of a manuscript that summarizes current knowledge on a given topic and synthesizes evidence from the results of research studies. Nearly all published research studies feature a background section that includes some form of literature review. The quality of the evidence depends on the thoroughness of the review. Individual research studies commonly include written literature reviews that are organized but not conducted using a specific method or orderly process.
Defining narrative review
A narrative, or expert, review typically is based on an author’s subjective selection of published articles addressing a specific question with a summary of findings and an implicit conclusion. Similar to a basic written literature review, a narrative review typically lacks methodology and an orderly process—meaning it allows author bias. It provides a broad overview of a selected topic and may include the author’s expert opinions. Normally, though, it doesn’t offer quantification or measurement. Narrative reviews usually aren’t identified in the hierarchies of evidence, but they’re considered to be among the lowest levels of evidence.
Defining integrative review
The term integrative review sometimes is used interchangeably with systematic review. Yet the two aren’t identical. An integrative review includes data from experimental and nonexperimental research studies as well as theoretical literature. It may serve a wide range of purposes, such as defining concepts, reviewing theories, or analyzing methodological issues. Typically, it uses an orderly, specified methodology and process but may lack true quantification of results. Integrative reviews usually aren’t found in the hierarchies of evidence but may be considered to provide a midlevel of evidence.
Defining systematic review
A systematic review uses a thorough, comprehensive process to identify and summarize all studies focused on a specific clinical question. Well-conducted systematic reviews are extremely exhaustive and typically involve several steps, including:
- asking an answerable question
- identifying all potential databases to search
- developing an explicit search strategy
- selecting titles, abstracts, and manuscripts based on explicit inclusion and exclusion criteria
- abstracting data in a standardized format.
Properly conducted systematic reviews use rigorous critical appraisal methods to assess the quality of each study and summarize the results using an objective process. Systematic reviews provide the highest level of evidence in any hierarchy. They reduce the potential for author bias that exists in narrative and integrative reviews. A properly conducted systematic review limits the possibility that the authors may choose studies arbitrarily considered the most relevant for supporting their own opinions or research hypotheses.
A meta-analysis is a statistical approach to mathematically combining the data derived from a systematic review. To put it another way, it’s a systematic review that uses established statistical methods to synthesize data from similar individual studies, for the purpose of integrating findings. The main reason for quantifying data from a systematic review is to increase the sample size and statistical power to determine the overall treatment effect of an intervention.
A meta-analysis can be applied only if all steps of a systematic review have been conducted properly. Results of meta-analyses offer the highest level of evidence. However, these reviews usually are the most complex and confusing to read.
The nurse’s responsibility
Given today’s emphasis on EBP combined with the economic environment in U.S. health care, translating research evidence into clinical practice is more important than ever. All nurses should be aware of and understand not just the origin of the evidence but the terms used and how the different types of literature reviews vary. Nurses at all levels can and should take responsibility for ensuring they have the best evidence available for making clinical decisions about patient care.
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Brian T. Conner is an assistant professor in the College of Nursing at the Medical University of South Carolina in Charleston.