Not to be confused with a book review, a literature review surveys scholarly articles, books and other sources (e.g. dissertations, conference proceedings) relevant to a particular issue, area of research, or theory, providing a description, summary, and critical evaluation of each work. The purpose is to offer a narrative or overview of significant literature published on a topic. There are various types of literature reviews, below are the most common.
A good resource to guide you through creating a systematic review is Cochrane Handbook for Systematic Reviews of Interventions which defines a systematic review (Section 1.2) as:
"...an attempt to identify, appraise and synthesize all the empirical evidence that meets pre-specified eligibility criteria to answer a given research question. Researchers conducting systematic reviews use explicit methods aimed at minimizing bias, in order to produce more reliable findings that can be used to inform decision making."
A literature review summarizes broad topic (ex: water pollution) using qualitative (narrative) methods by incorporating a variety of sources. It may be assigned as a stand-alone project for a class where you are asked to examine literature or sources around a specific; or part of a larger body of work such as a thesis or dissertation where you examine literature and how it connects to your research. It is commonly used across all disciplines, for all levels of scholarship (undergrad, graduate and professional).
A systematic literature review answers a specific question (ex: Are micro plastics in drinking water a contributing factor for an increase in cancer in urban populations?) through a structured format such as PICO or PRISMA. It will demonstrate your search strategy along with information about what was included/excluded and why. It is highly technical, and may be used by graduate students, experts and professionals across all disciplines.
A meta-analysis literature review looks at studies from a systematic review, combining the studies in order to collect data and get a statistically relevant result. This type of review is helpful in using statistical analysis to examine or overturn results from smaller clinical trials. It is highly technical, and typically used by experts and professionals in medical fields.
A mapping/scoping review seeks to provide an overview of the available research evidence without producing a summary answer to a discrete research question. It is a newer method of literature review analysis and is used across all disciplines, but more specifically in medical sciences.
A comprehensive literature review helps you build a case for your own research and helps you base your research on a strong scholarly foundation. You will need to review the materials you have collected and the feedback received by your cohort. Then, identify any gaps in your research. Conduct and in-depth literature review using bibliographies and references lists from sources you have already collected. Use tools like Web of Science to track highly cited/landmark articles and to find related articles. Search using Library Search, databases, theses and dissertations, and more.
An umbrella review compares and contrasts the findings of previous reviews relevant to a review question. An umbrella review synthesizes only the highest level of evidence - other systematic reviews and meta-analyses.
A rapid review speeds up the systematic review process by omitting some stages of the systematic review. While less rigorous, rapid reviews provide more timely information for clinical decision making compared with standard systematic reviews.
|Literature Review||Systematic Review|
|Provides an overview of a topic||Examines a clearly defined topic or question|
|Does not use an explicit search protocol or plan||Uses an explicit search plan or protocol to minimize bias|
|The search process may or may not include all potentially relevant studies||A comprehensive search is undertaken to identify all potentially relevant studies|
|An explicit, predetermined protocol is not used to select the studies that are used to support the reviewers' recommendations||An explicit, predetermined protocol, that specifies inclusion and exclusion criteria, is used to select studies for the review|
|A level of evidence rating system may be used to "grade" the quality and strength of individual studies||The quality of individual studies is rigorously appraised in a meta-analysis and a systematic synthesis of the results of included studies is undertaken with evidence "grades" applied to individual studies|
|May be evidence-based, but is not evidence (research)||Provides evidence (research)|
|When evidence is lacking, the authors make recommendations based on their opinions and experience||When evidence is lacking, the authors usually recommend further research|
Step 1: Problem Formulation - Identifying a Research Question
The most common mistake one might make when conducing a literature review is to start searching for answers with only a vague idea of what information is needed. Well-formed questions underpin the very core of scientific methodology and a clear scholarly statement or research question should be identified before you begin. One cannot get a clear answer to a vague question.
Use frameworks such as the 5Ws (Who - What - When - Where - Why) or PICO (Problem/Patient/Population - Intervention - Comparitor - Outcome) to explore all aspects of your topic before you begin dedicating yourself to searching and synthesizing information.
PICO It is typically used for evidence-based medicine whereas the 5Ws are used widely in other disciplines. Using a framework to map out your research question will help you to ensure that your search for evidence is structured, systematic and complete.
Step 2: Literature Search
Once you have a clear idea about what you want to research, begin identifying key studies, sources, databases, reports and books to use. Multiple resources should be searched (example, no less then 3 databases) and grey literature should be included in order to reduce publication bias. As you are searching, use a citation management program such as Zotero and/or research log to track sources. Use this example spreadsheet to get started. Using a research log will help to:
Step 3: Data Evaluation
This involves a quality assessment of the sources selected and is relevant to every step of a review. When doing this step, you are determining which literature makes a significant contribution to the understanding of the topic. The risk of publication bias and related biases should also be explored. Any recommendations should be considered in connection to its strengths and weaknesses of evidence.
Step 4: Analysis and Interpretation
This final steps will be your narrative of the findings and any conclusions of pertinent literature and may also data tabulation.
The purpose of a systematic review is to answer a clear and focused question. Translating a knowledge gap into an answerable and soundly constructed question is an important skill. The review question should be defined at the beginning your systematic review. A well formulated review question will help determine your inclusion and exclusion criteria, the creation of your search strategy, the collection of data and the presentation of your findings. A sound clinical question:
The question should always be:
It is important to formulate your research question with care so as to avoid missing relevant studies or collecting a potentially biased result set. To do that, use a framework such as the 5Ws (Who - What - When - Where - Why) or PICO (Problem/Patient/Population - Intervention - Comparitor - Outcome) to explore all aspects of your topic before you begin dedicating yourself to searching and synthesizing information. PICO It is typically used for evidence-based medicine whereas the 5Ws are used widely in other disciplines. Using a framework to map out your research question will help you to ensure that your search for evidence is structured, systematic and complete.
PICO or PICo are useful tools for defining clear, focused clinical questions and developing a review protocol. Before defining your question using PICO or PICo, you should check that your question has not already been the subject of a systematic review.
What if you want to change things later?
A protocol for a systematic review should only be modified if it becomes clear that there are alternative ways of defining your population, intervention, outcomes or study designs.
|Population or Problem||Intervention or Exposure||Comparison||Outcome|
What are the characteristics of the population or patient?
What is the problem, condition or disease you are interested in?
|How do you wish to intervene - what do you want to do with this patient - treat, diagnose, observe, etc.?||What is the comparison or alternative to the intervention - placebo, different drug or therapy, surgery, etc.?||What are the possible outcomes - morbidity, death, complications, etc.?|
To develop an effective search strategy, use the PICO worksheet below.
This includes identifying:
Here is an example of a clinical question that outlines the PICO components:
P = middle-aged male amputee suffering from phantom limb
I = is gabapentin
C = compared with placebo
O = effective in decreasing pain symptoms?
Literature reviews should comprise the following elements:
In assessing each piece for selection, consider: