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Literature Searches and Literature Reviews: Literature Reviews

Literature Reviews

Literature reviews are critical portions of the research process and important components of final research reports. In transportation research, the best approach to a literature review is complicated by the wide range of business functions and research subject areas falling under the jurisdiction of federal and state transportation agencies. In addition, the applied nature of most state-sponsored research often means the project scope is already well-defined by the customer and not as open-ended as some academic research.

Note that a literature review is more than a bibliography (a list of published works with author, publisher, date, etc.) or an annotated bibliography (a summary or evaluation of each work). It's a narrative, organized by topic, that draws connections among citations and presents cited works according to their importance and relevance.

A literature review is completed in six steps:

  • Step 1: Conduct a literature search.
  • Step 2: Determine the purpose of the literature review.
  • Step 3: Determine the scope of the literature review.
  • Step 4: Review the research.
  • Step 5: Evaluate the research.
  • Step 6: Organize the material and write the literature review.

Highlights from each of these steps are presented in this section. For a more detailed discussion of each step, review the "Literature Reviews: How to Put It All Together" section of Transportation Research E-Circular 194: Literature Searches and Literature Reviews for Transportation Research Projects

Step-by-Step Guide

Value of a Literature Review

  • Informs a research project. Provides insight into a topic by identifying what is and isn’t known about a research topic, including areas of controversy and questions that require further research. The process can also steer researchers away from previous approaches that have been unsuccessful.
  • Provides context. Summarizes the current state of research about a topic and previous work on related topics. The literature review helps to define the scope of an investigation, examining assertions made in existing literature and synthesize the literature to present a new perspective.
  • Establishes authority. Demonstrates the researcher’s understanding of knowledge and research on a given topic. 

Types of Literature Reviews

Below are several types of literature reviews used to classify citations:

  • Focus. Reviews can focus on research outcomes, research methods, theories, and practices or applications. Most reviews will focus on more than one of these areas.
  • Goals. Goals include synthesis, criticism and identification of central issues. Nearly all reviews synthesize past literature.
  • Perspective. Literature reviews can either present evidence neutrally or advocate for a specific position. 
  • Coverage. Reviews may be:
    • Comprehensive, presenting all works relevant to the topic.
    • Comprehensive with selected citations, basing conclusions on all works relevant to the topic, but only presenting the most important works.
    • Representative, presenting samples of the relevant material.
    • Concentrated on central or pivotal works.
  • Organization. Reviews can be organized chronologically, conceptually or methodologically. More details about organization options and the scenarios where each is most appropriate are presented in Step 6.
  • Audience. The writing style and language used in a review will vary depending on the audience—whether specialized researchers, general researchers, practitioners, policymakers or the general public.

See Steps 2 and 6 for more information about these topics.

Another classification method is based on whether the subject is relatively mature or still emerging. In mature topics, a literature review analyzes and synthesizes existing literature, with the ultimate goal of proposing a model that extends that research. In emerging topics, a literature review presents the theoretical foundations of the research at hand.

Step 1: Conduct a Literature Search

See Literature Searches: Step-by-Step Guide for information about how to conduct a literature search and the resources to use in the search. Each step in the literature review writing process may inform a need to revisit and expand the literature search.

Step 2: Determine the Purpose of the Literature Review

  • What is the goal of the review? In additions to synthesizing information, literature reviews may analyze existing literature to demonstrate which conclusions are warranted or to identify issues central to a field, such as methodological problems that have blocked progress in a specific topic or areas of inquiry that have been or should be the focus of research.
  • Who is the audience? The writing style and language chosen will change, depending upon whether the literature review is aimed at specialized researchers, general researchers, practitioners, policymakers or the general public.
  • What is the focus of the review? Is the focus on research outcomes, research methods, theories, or practices and applications? These topics are not mutually exclusive, and many reviews will address more than one area.
  • What is the perspective of the review? A literature review may present information neutrally, or it may build a case for a specific position. (Note that this can be achieved without bias; an author should present conflicting evidence and interpret it fairly.)

Step 3: Determine the Scope of the Literature Review

To determine the scope:

  • Define the specific topic that the literature review will cover and topics that will not be covered.
  • Determine how comprehensive the review will be. It may be appropriate to seek all relevant works, a representative sample or only the significant works on a topic.
  • Define the time period the review will cover. Literature reviews that seek to synthesize current knowledge often focus on recent research, while reviews that seek to demonstrate how a field has developed over time will naturally incorporate more historical research.

Step 4: Review the Research

Keep detailed notes about the bibliographical information of relevant research. A University of Colorado–Denver tutorial (see Resources at right) presents two approaches to note-taking:

  • The “summarize-as-you-go” method: The researcher writes complete sentences with citations that can be pasted into the literature review nearly verbatim. These notes should summarize a study’s context, methods, findings, conclusions and implications.
  • The “note-basic-details” method: The researcher captures  basic information about a study’s context, methodology, findings, implications and suggestions for future research without trying to generate nearly publication-ready prose. Prevalent themes in individual studies should also be noted so they can be compared and organized when all studies have been reviewed.

The former method requires more work early in the process, while the latter requires more effort later.

Step 5: Evaluate the Research

Use the six-step framework below to process the information gathered:

  • Know the material. Understand the information in each cited work and the methodology used to reach its conclusions instead of simply identifying works that are relevant without describing their conclusions.
  • Comprehend the material. Demonstrate the significance and relevance of a cited source to the topic instead of simply repeating the information within the source.
  • Apply the material. Identify the major concepts of each work cited that relate to the study and organize the information so that it can support the literature review.
  • Analyze the material. Demonstrate the value of the information cited instead of simply presenting it and leaving the reader to draw conclusions.
  • Synthesize the material. Present the information as a narrative, not a collection of facts, and note any gaps in knowledge and areas of dispute.
  • Evaluate the material. Distinguish between the facts, theories and opinions in the works cited instead of presenting each source has having equal supporting evidence and validity.

Source: "Towards a Framework of Literature Review Process in Support of Information Systems Research," Y. Levy  and T. Ellis, Proceedings of the 2006 Informing Science and IT Education Joint Conference, 2006.

Step 6: Organize the Material and Write the Literature Review

Organizing the content in a logical, thematic manner that supports the literature review’s overall goals is critical. Some common methods for organizing cited works include:

  • Chronological, to show how knowledge in a field grows and changes over time.
  • Descriptive, to highlight themes, presenting and analyzing the work of several authors.
  • Descriptive–analytical, to present the similarities and differences among the sources instead of presenting them at the end.
  • Big-to-small-to-big, to highlight how the results of broader studies differ from smaller ones. These reviews begin with the largest, most wide-ranging studies before progressing to smaller ones and then branching out to larger studies, and is particularly useful for empirically oriented reviews.
  • Methodological, to group studies by the methodologies that were used. A brief analysis after each methodology describes what is covered, while a master analysis at the end compares and summarizes the findings.
  • Big camps, to illustrate distinct interpretations of a set of data. These reviews can either present various topics and how the different camps’ interpretations are similar for each, or present each camp and its interpretations of all relevant themes as a single unit.

A literature review may use more than one of these methods if appropriate. However, presenting literature author by author—that is, presenting the full content of one paper, followed by the full content of the next and so on without synthesizing the information and showing the relationships between various authors’ work—is discouraged.

Additional Resources

The appendices below appear in Transportation Research E-Circular 194: Literature Searches and Literature Reviews for Transportation Research Projects. Page references follow each appendix title. 

Appendix A, Examples of Effective Transportation Literature Reviews (beginning on page 27)

  • Reports that are primarily literature reviews, with little or no additional research: Crack and Concrete Deck Sealant Performance; Snow Removal at Extreme Temperatures
  • Reviews that are smaller portions of a project, intended to frame or inform a problem: Development of a Concrete Maturity Test Protocol; Quality of Life: Assessment for Transportation Performance Measures 

Appendix B, Tutorials on Writing Literature Reviews (beginning on page 29)

Appendix C, Examples of an Annotated Bibliography (beginning on page 31)

Appendix D, Draft Specification Language (beginning on page 34)

Appendix E, Literature Resources: Where to Search (beginning on page 35; resources in this appendix are also listed in the Resources: Where to Search section of this guide)

Appendix F, Definitions (beginning on page 70)

Resources

"Analyzing the Past to Prepare for the Future: Writing a Literature Review," J. Webster and R. Watson, MIS Quarterly, Vol. 26, No. 2, June 2002, pages xiii–xxiii.

Educational Research: An Introduction, 6th edition, M. D. Gall, W. R. Borg and J. P. Gall, Longman, White Plains, New York, 1996.

"Guide to Writing the Dissertation Literature Review," J. A. Randolph, Practical Assessment, Research & Evaluation, Vol. 14, No. 13, June 2009.

Guidelines for Abstracts, ANSI/NISO Z39.14-1997, NISO Press, Bethesda, Maryland.

How to Conduct a Literature Review, J. Mattson and D. Ripplinger, presented at Transportation and Logistics Seminar, Small Urban & Rural Transit Center, Upper Great Plains Transportation Institute, December 1, 2008.

Introduction to Library and Literature Research for Transportation, R. Bertini, Portland State University, Portland, Ore., 2012.

"‘It’s a PhD, Not a Nobel Prize’: How Experienced Examiners Assess Research Theses," G. Mullins and M. Kiley, Studies in Higher Education, Vol. 27, No. 4, 2002, pages 369–386.

The Literature Review: A Few Tips on Conducting It, D. Taylor, Health Sciences Writing Centre, University of Toronto, undated.

"Organizing Knowledge Syntheses: A Taxonomy of Literature Reviews," H. Cooper, Knowledge in Society, Vol. 1, 1988, pages 104–126.

"Scholars Before Researchers: On the Centrality of the Dissertation Literature Review in Research Preparation," D. N. Boote and P. Beile, Educational Researcher, Vol. 34, No. 6, August–September 2005, pages 3–15.

Scientific Approaches to Transportation Research, S. Washington, J. Leonard, D. Manning, C. Roberts, B. Williams, A. Bacchus, A. Devanhalli, J. Ogle and D. Melcher, NCHRP Report 20-45, Vols. 1 and 2, 2001.

"Towards a Framework of Literature Review Process in Support of Information Systems Research," Y. Levy and T. Ellis, Proceedings of the 2006 Informing Science and IT Education Joint Conference, 2006.

Writing a Literature Review, University of Colorado Denver School of Public Affairs, undated.