W1A. Literature Review Introduction, Research Gap, Systematic Search

1. Summary

1.1 What is a Literature Review?

A literature review (LR) is an overview of the available research for a specific scientific topic. Rather than presenting new experimental data, a literature review synthesizes what has already been discovered, debated, and published by other researchers. Think of it as a map of existing knowledge: it shows you what territory has been explored, where the paths are well-traveled, and—most importantly—where the unexplored regions lie.

Literature reviews appear in academic writing in three distinct forms, depending on how much of the overall document they occupy:

• Background section: A short review embedded at the beginning of a research paper to provide context. It occupies only a small portion of the full document.
• Part of a research project write-up: A more substantial review that forms one chapter or section of a larger study (e.g., a thesis or journal article).
• Stand-alone product: An entire paper dedicated solely to reviewing and synthesizing the literature on a topic. This is the most comprehensive form and the focus of this course.

1.1.1 The Literature Review Workflow

Writing a literature review is not a single step but a structured process:

1. Select your interest: Choose a topic or field you wish to investigate.
2. Find a research gap: Identify what information is missing, contradictory, or underexplored in the existing literature.
3. Formulate a research question or goal: Define precisely what your literature review will answer or accomplish.
4. Design your literature search: Select appropriate academic databases and construct a search string using Boolean operators.
5. Conduct the search: Retrieve sources following defined inclusion and exclusion criteria.
6. Analyze and synthesize: Read, evaluate, compare, and summarize the findings across your selected sources.

1.2 The Research Gap

The research gap is the starting point of any meaningful literature review. It is the space in the existing body of knowledge that your review will attempt to fill. Without a clearly identified research gap, your literature review has no justification for existing.

A research gap exists under several conditions:

• Missing or insufficient information: The topic has not been studied enough, or the available studies are too narrow in scope.
• Biased or one-sided information: Existing studies consistently examine only one perspective, leaving alternative viewpoints unexplored.
• Contradictory results: Different studies reach opposing conclusions, and no consensus or reconciliation exists in the literature.
• Inadequate overview: The topic has been studied in pieces, but no comprehensive synthesis bringing everything together has been produced.

Important: The research gap does not just justify your study—it actively shapes how you will explore the literature. It determines what you look for, what databases you search, and how you frame your research question.

1.2.1 Finding a Research Gap

To find a research gap, follow these steps:

1. Pick a field or topic of genuine interest. Motivation matters in a long research process.
2. Search the literature broadly in that field to understand what has already been done.
3. Look for absence: What questions remain unanswered? What populations, time periods, or perspectives have been ignored? Where do studies disagree?

1.3 Systematic Search

Once you have identified a research gap, you need to locate all relevant sources in a rigorous, reproducible way. This requires a systematic search—a methodical procedure for finding literature that minimizes bias and maximizes comprehensiveness.

1.3.1 Why Systematic Search Matters

Not all search strategies are equal:

• Random search depends on chance. You find what happens to come up, not necessarily what is most relevant or complete.
• Snowballing (following citations backward or forward from an initial source) is biased toward papers that are already widely cited and misses newer or less prominent work.

A systematic search, by contrast, is designed to be comprehensive, replicable, and transparent. Anyone following your documented procedure should be able to arrive at the same pool of sources.

1.3.2 Choosing a Database

Use academic databases that support advanced Boolean search—databases that let you combine search terms with logical operators (AND, OR, NOT) and apply filters:

• ScienceDirect
• IEEE Xplore
• ACM Digital Library
• Dimensions AI
• OpenAlex

Avoid databases that do not produce replicable results or that include non-peer-reviewed sources:

• Google Scholar (results vary by user and session)
• arXiv (preprints, not peer-reviewed)
• ResearchGate, Academia.edu (social media platforms for researchers)

1.3.3 Building a Search String

A search string is a structured query you enter into a database to retrieve relevant papers. It uses Boolean operators to combine keywords:

• OR connects synonyms (finds papers mentioning any of the terms)
• AND connects concepts (finds papers mentioning all of the concepts)
• Quotation marks ensure exact phrase matching

Example topic: Ethics of using autonomous vehicles.

Search string template:

("main topic" OR "synonym 1" OR "synonym 2") AND ("aspect 1" OR "aspect 2") AND ("review" OR "literature review")

Full example:

("autonomous vehicle*" OR "self-driving vehicle*" OR "driverless car*" OR AV)
AND (ethic* OR moral* OR "trolley problem*" OR "decision making" OR accountability)
AND (review OR "literature review")

Breakdown of this string:

• First group (OR): All synonyms for the main concept (autonomous vehicles). The asterisk * is a wildcard that matches any ending (e.g., ethic finds “ethics,” “ethical,” “ethically”).
• Second group (OR): All relevant aspects of the topic (ethical dimensions).
• Third group (OR): Restricts results to review-type papers, ensuring you find literature reviews rather than primary studies.

The goal of the search string is to be broad enough to capture all relevant papers while narrow enough to exclude obviously irrelevant ones.