Chapter 6

1. Chapter 6 Reviewing the Literature

2. Learning Objectives • Explain the purposes of the literature review • Describe the elements of the review • Conduct a literature search • Write a literature review

3. What is the Literature Review? • A summarized document that describes and critiques the past and present state of information about a certain topic

4. 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

5. Conducting the Review • Locate relevant studies • Select relevant studies • Organize relevant studies • Summarize the relevant content of the studies

6. Locating the Relevant Studies • Strive to be as thorough as possible and appropriate • Consider published and unpublished studies • Search a variety of sources

7. 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

8. 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literature searches • Advantage • Timely current information • Disadvantage • Questionable quality if journal is not peer-reviewed

9. 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

10. 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

11. 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

12. 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

13. Organize Relevant Studies • Several different methods • Tabular form is useful • An example follows

14. Tabular Organization

15. 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

16. 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

17. 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

18. Thematic Organization • Components of a conceptual picture of the overall results of the studies • Can be illustrated in an outline format

19. Example Outline Format • Diabetes Mellitus • Type 2 diabetes in children and adolescents • Epidemiology • Diagnosis • Associated Factors • Relationship to obesity • Other risk factors: puberty, ethnicity, gender, hypertension, metabolic syndrome • Treatment of Type 2 diabetes in children and adolescents • Assessment of control in diabetes • Definition of control • Glycemic control • Lipid management • Determinants of diabetes control • Socio-demographic factors • Biomedical factors • Self-care behaviors • Medications • Home diabetes status monitoring • Exercise • Diet • Weight control • Education

20. Example Outline (cont.) • Themes for example outline of diabetes • Description and justification of the problem • Control Strategies • Risk Factors

21. 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

22. Example Thematic Review Significance 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).”

23. 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)

24. Tips for Preparing the Review • make the review reasonably exhaustive, • include only relevant studies, • use recent studies as appropriate, • analyze as well as summarize the studies, • organize the summary in some meaningful way, typically by themes, and • emphasize the path from results of prior studies to the potential contribution of the present study.