Chapter 6

Reviewing the Literature

Learning Objectives

• Explain the purposes of the literature review• Describe the elements of the review• Conduct a literature search• Write a literature review

What is the Literature Review?

• A summarized document that describes and critiques the past and present state of information about a certain topic

Importance of the Review• Link between existing knowledge and the

problem of interest• Places the current study in the scientific

method for understanding the problem of interest

• Informed procedure for refining the research method

• Helps assure that the current study will truly make a contribution to the specific field

Conducting the Review

• Locate relevant studies• Select relevant studies• Organize relevant studies• Summarize the relevant content of the studies

Locating the Relevant Studies

• Strive to be as thorough as possible and appropriate

• Consider published and unpublished studies• Search a variety of sources

Sources of Information• Books– Advantages• Efficient source for a lot of information• Theories, methodologies, measures, background

information such as pathophysiology of medical conditions• List of the book’s references can be used as a starting

point for branching bibliographies (one source cites a source to inspect, which cites another source to inspect, and so on)

– Disadvantage• Not usually timely or current

Sources of Information (cont.)• Journal Articles– Primary Source - original research-based studies

published in a peer reviewed journals– Secondary Source - review articles summarize the

existing knowledge on a particular topic based on extensive literature searches

– Advantage• Timely current information

– Disadvantage• Questionable quality if journal is not peer-reviewed

Sources of Information (cont.)• Databases

– Searchable organized collection of research results– Bibliographic Databases

• Most common type in medical research• Contains information on books, reports, citations, abstracts, and either full

text articles or a links to the full text• PubMed is popular database for medical research

– Citation Databases• Facilitate the tracking of all published research that has been done to date

on a particular research topic• ISI Web of Knowledge is one of the most popular citation database

– Synthesized Databases• Pre-filtered records for particular research topics• Access mostly by subscription and relatively expensive• Cochran Collaboration, National Guideline Clearinghouse, and UpToDate

are popular examples

Filtering Out the Irrelevant• Careful choice of keywords– Target population of the study: youth, hospital

patients, immigrants– Study methodology: case-control, randomized

controlled trial, ethnography– Exposure or risk factor: obesity, low socioeconomic

status, living near a nuclear power plant– Outcome: diabetes, alcohol abuse, pancreatic cancer– Specific measures: BMI, stress, zip codes– Analytic strategy: life table, logistic regression,

content analysis

Filtering Out the Irrelevant (cont.)

• Necessary parameters for inclusion– Use these as keywords to start– Examples• Only recently published articles• Only randomized controlled trials• Only studies in the U.S.• Only older adults

Selecting Relevant Studies

• As part of the search, review the results– Title– Abstract– Main Headings

• Obtain full-text articles of those that seem relevant– Some full-texts are available through the search

engine– Most are available through a university library

Organize Relevant Studies

• Several different methods• Tabular form is useful• An example follows

Tabular OrganizationStudy Methodology Results Strengths Weaknesses

1. Bailey, 1992

Cohort4192 secondary school studentsSurvey- 3 wavesPatterns of drug usePercentagesDescriptive

Escalation of illicit substances is associated with continued use and initiation of illicit substances

CohortLarge NTransitionsCareful analysis

No causal factors testedSelf reportsAttrition of heavier usersLimited to SE US

2.

3.

4.

Tabular Organization (cont.)• Each row is a study• “Study” column identifies which study is being

summarized for reference to the original article• “Methodology” column summarizes important

features of the study design• “Strengths” indicate the relevance of the study• “Weaknesses” suggest what the new study might

add• Other potentially useful columns– Purpose of the study– Specifically what this study will contribute to the new one

Summarize the Relevant Content• Introduction– Define the topic– State the purpose– Present the significance

• Body of the Review– Summary and analysis of the studies

• Conclusion– “Lesson” learned from the review– Relevant contribution of the new study

Body of the Review

• Organized by Theme– Typical organization for research studies

• Organized by Historical Time– Time that the studies took place or period under

study• Organized by Study Design/Methodology– For example, experimental and non-experimental

• Organized by Type of Target Population– For example, various age groups, stages of disease

Thematic Organization

• Components of a conceptual picture of the overall results of the studies

• Can be illustrated in an outline format

Example Outline Format I. Diabetes MellitusII. Type 2 diabetes in children and adolescents

1. Epidemiology2. Diagnosis3. Associated Factors

a. Relationship to obesityb. Other risk factors: puberty, ethnicity, gender, hypertension, metabolic syndrome

4. Treatment of Type 2 diabetes in children and adolescentsIII. Assessment of control in diabetes

1. Definition of control2. Glycemic control3. Lipid management

IV. Determinants of diabetes control1. Socio-demographic factors2. Biomedical factors3. Self-care behaviors

a. Medicationsb. Home diabetes status monitoringc. Exercised. Diete. Weight controlf. Education

Example Outline (cont.)

• Themes for example outline of diabetes– Description and justification of the problem– Control Strategies– Risk Factors

Summarize the Relevant Content of the Studies

• Thematic review of literature focuses on a theme and, in a succinct manner, cites multiple studies to document important findings under each theme

• Major results of the studies are summarized rather than the details about each study

• Typically report a particular finding and cite multiple references in parentheses after

Example Thematic ReviewSignificance of the problem: “Case studies in Ohio, South Carolina and a few other states have shown increasing percentages of incident pediatric cases of diagnosed diabetes, with fewer than 4% reported before 1990s and up to 45% in recent studies (Pinhas-Hamiel et al., 1996; Willi et al., 1997; Fagot-Campagna et al., 2000).Risk factors: Those believed to be at greatest risk are minority children (Native, African, and Mexican-Americans) who are obese, inactive, and genetically predisposed to the development of Type 2 diabetes (Dabelea et al., 1999).”

Citations and References

• Statements that are not common knowledge should be cited

• Results of studies are an example of statements that always should be cited

• Styles most often used in epidemiology– American Medical Association (AMA)– American Psychological Association (APA)

Tips for Preparing the Review

1) make the review reasonably exhaustive,2) include only relevant studies,3) use recent studies as appropriate,4) analyze as well as summarize the studies,5) organize the summary in some meaningful

way, typically by themes, and6) emphasize the path from results of prior

studies to the potential contribution of the present study.