A literature review is a synthesis of the literature on a topic. To create the synthesis, various diverse and sometimes conflicting ideas and findings in the literature need to be evaluated and combined to create a new, original work that provides an organized overview of the state of knowledge on a topic.
A literature review critically examines and summarizes the literature on a chosen topic. The reviewer evaluates the available evidence and relevant theories while noting gaps in the literature, and creates a snapshot of the state of research in a particular topical area. The first challenge of the literature review is in identifying the topic and the boundaries around what literature to review. The second challenge is to understand what information in each item reviewed is relevant to the literature review. The third challenge is writing about it in a clear and thorough way.
Qualitative and Quantitative Literature Reviews
Qualitative and quantitative reviews do not form a dichotomy. Rather, literature reviews exist on a continuum from highly qualitative (with little mention of statistics or research methods) to highly quantitative (with the final synthesis based on the mathematical averaging of results across various studies reported by different researchers).
Most beginning students should consider writing a qualitative review in which statistical material is judiciously selected for inclusion in the review. Future chapters will explain how to select and interpret such statistical material and how to present it in qualitatively oriented reviews.
Types of Literature Reviews
Literature reviews are created for several purposes. They can stand alone as review articles, which help to inform academics, or in some cases, nonprofit, government or other practitioners, about important current topics and developments in a discipline. However, students are likely to first (and more frequently) encounter literature reviews as a section of another piece of work. Literature reviews are a component in research articles and academic works, such as theses and dissertations. The length and depth of a literature review varies based on its purpose and the constraints for where it appears. For instance, empirical articles are limited to specific word counts by publications, so the literature review is quite brief. In theses and dissertations, literature reviews constitute an important section or chapter which must show mastery that supports the research and fulfills the requirements related to the degree. Review articles that stand on their own tend to be longer than those within articles, but the length may also be constrained by factors such as publication length limits. Despite these differences, the purpose of a literature review are largely the same.
Abstracts Versus Literature Reviews
An abstract is a brief summary of a published work. Most research articles in professional journals begin with abstracts, which are typically about 150 to 250 words in length. Stringing together a series of abstracts on a given topic does not create a literature review because such a string of elements fails to organize and show how various elements in the literature relate to each other.
Overview of Steps in Preparing a Literature Review
The following steps are described in more detail in the remaining chapters of this book. These steps apply to both qualitative and quantitative reviews. The distinction between the two types of reviews is explored later in this chapter. The steps presented here are comprehensive for creating a stand-alone literature review, but when a literature review is being created as part of an article or a larger academic work, some steps may be less relevant. For instance, when a literature review is prepared for an empirical article, the first step of selecting a topic may already be defined based on the research. However, there may still need to be some choices about what to include in the literature review to define the relationship between the research and the existing literature.
Step 1: Select a Topic
The first step is to select a topic. In most cases, this is an interactive process in which the initial search of the literature reveals how much and what types of literature exist on a topic. Based on this information, the initial topic may need to be narrowed, broadened, or adjusted. At the same time, the needs of the audience for whom the review is being written will influence the selection of a topic.
Step 2: Locate and Read Literature for an Overview
The second step is to locate literature on the selected topic and read it with an eye toward getting a broad overview of which issues have been thoroughly covered, which ones need more investigation, which principles seem most firmly established and/or most widely accepted as being valid, and, perhaps most important, which theories have a bearing on the topic being reviewed.
Step 3: Establish Specific Purposes
Third, the reviewer should establish specific purposes for the literature review. For instance, Box 1A
shows some possible purposes. Note that the purposes should be put in writing, which can later be incorporated into the introduction to the literature review. In addition, a student who is preparing a literature review for a class might share the written purposes with the instructor in order to get feedback on their appropriateness before beginning to write the review.
The first three steps are likely to be iterative. This means that the reviewer is likely to jump between these tasks because they will inform and improve the other. When selecting a topic, it is likely that the reviewer will locate and read literature, which will help to establish specific purposes, and narrow the selected topic, leading to further literature.
The purposes of this literature review are to
- Trace the history of scientific developments, including relevant theories, that resulted in the development of Treatment X;
- Summarize and evaluate the legal and ethical issues involving the implementation of the treatment;
- Estimate the overall degree of effectiveness of the treatment by evaluating the experiments in which the treatment was compared with a placebo; and
- Describe possible fruitful areas for future research based on the research conducted to date.
Step 4: Evaluate and Interpret the Literature
Next, the literature needs to be evaluated and interpreted. Many reviewers give high evaluations to sources that present the results of rigorous scientific studies. At the same time, many reviewers give high evaluations to studies that provide crucial insights even if the underlying methods for collecting data are mildly, or even seriously, flawed. In addition, all authors of literature reviews should pay special attention to literature that presents, tests, and/or builds on the theories related to their topics.
Step 5: Synthesize the Literature
Fifth, the literature needs to be synthesized. This is done by first grouping various sources according to their similarities and differences, while considering possible explanations for differences (and contradictions) in the literature. Note that a synthesis very often will not result in a single, straightforward conclusion. Instead, it might consist of speculation on how the pieces of evidence found in the literature fit together along with some tentative conclusions and a discussion of their implications. This often leads to suggestions for future research that might produce a more definitive understanding of the topic.
Step 6: Plan and Write the First Draft
Most reviewers begin by introducing the topic and establishing its importance (e.g., indicating how many individuals are affected by the issue under review). Then, they prepare a topic outline with major headings and subheadings and write the review following the outline.
Step 7: Have the First Draft Evaluated and Revise It
The first draft of a literature review should be evaluated by others. Of course, an evaluation by an expert is highly desirable. However, note that a well-written review should be comprehensible even to nonexperts, such as other students, who can often provide valuable feedback. Revising (and, in some cases, entirely rewriting) a review in light of this feedback is a crucial step in producing a literature review of high quality.
This book covers the preparation of both qualitatively oriented and quantitatively oriented reviews. The following guidelines help distinguish between the two types of reviews.
Guideline 1.1: Quantitatively oriented reviewers place more emphasis on precise statistical results than do qualitatively oriented reviewers.
The main distinction between the quantitatively oriented and qualitatively oriented reviews lies in the extent to which specific statistics are used in creating a synthesis. Reviewers who write quantitatively oriented reviews base their synthesis and conclusions more closely on specific statistical values than do those who write qualitatively oriented reviews. For instance, compare the statement in Example 1.1.1 with the one in Example 1.1.2. Note that the statements in both examples refer to the same three published experiments.
Sample statement that might appear in a quantitatively oriented review
The three experiments in which Drug A was compared with a placebo yielded mean reductions on the Pain Relief Scale of 2.1, 3.3, and 4.0 points on a scale from 0 (no pain
) to 20 (extreme pain
). All three were statistically significant at the p <
.05 level. The mean (i.e., arithmetic average) of these three means is 3.1, which is the best estimate of the effectiveness of Drug A. Hence, Drug A appears to produce a small but significant reduction in pain.1
Sample statement that might appear in a qualitatively oriented review
In each of the three experiments in which Drug A was compared with a placebo, there was a small but significant reduction in pain reported by those who took the drug, as indicated by self-reports on the Pain Relief Scale. On this 20-point scale, the average for the experimental group was a few points lower than the average for the placebo group. Thus, Drug A appears to be effective but of limited value in reducing pain.
In summary, authors of highly quantitatively oriented reviews tend to cite precise statistical values, while authors of qualitatively oriented reviews often make only general references to statistical findings.
Guideline 1.2: If the main thrust of a review is the mathematical combination of statistics, the review is called a meta-analysis or meta-analytic review.
The prefix meta
means going beyond
refers to a statistical analysis that goes beyond or transcends previous statistical analyses. For
instance, the author of Example 1.1.1 used the meta-analytic technique of averaging results across three studies.
The use of meta-analytic techniques (such as averaging means or correlation coefficients across studies) is most likely to be found in quantitatively oriented reviews. There is no reason, however, why the author of a primarily qualitatively oriented review could not occasionally use such a technique to make his or her review more quantitatively oriented than it otherwise would be. Thus, readers who are planning to write qualitatively oriented reviews should carefully study the material on meta-analysis in the last two chapters of this book.
Guideline 1.3: Qualitative and quantitative reviews have many common features.
The authors of both qualitatively oriented and quantitatively oriented reviews have an obligation to cover certain common ground, including the following:
- introducing the topic and defining key terms;
- establishing the importan...