A literature review is a critical analysis of published academic literature, mainly peer-reviewed papers and books, on a specific topic. This isn’t just a list of published studies but is a document summarising and critically appraising the main work by researchers in the field, the key findings, limitations and gaps identified in the knowledge.
- The aim of a literature review is to critically assess the literature in your chosen field of research and be able to present an overview of the current knowledge gained from previous work.
- By the conclusion of your literature review, you as a researcher should have identified the gaps in knowledge in your field; i.e. the unanswered research questions which your PhD project will help to answer.
- Quality not quantity is the approach to use when writing a literature review for a PhD but as a general rule of thumb, most are between 6,000 and 12,000 words.
What Is the Purpose of a Literature Review?
First, to be clear on what a PhD literature review is NOT: it is not a ‘paper by paper’ summary of what others have done in your field. All you’re doing here is listing out all the papers and book chapters you’ve found with some text joining things together. This is a common mistake made by PhD students early on in their research project. This is a sign of poor academic writing and if it’s not picked up by your supervisor, it’ll definitely be by your examiners.
The biggest issue your examiners will have here is that you won’t have demonstrated an application of critical thinking when examining existing knowledge from previous research. This is an important part of the research process as a PhD student. It’s needed to show where the gaps in knowledge were, and how then you were able to identify the novelty of each research question and subsequent work.
The five main outcomes from carrying out a good literature review should be:
- An understanding of what has been published in your subject area of research,
- An appreciation of the leading research groups and authors in your field and their key contributions to the research topic,
- Knowledge of the key theories in your field,
- Knowledge of the main research areas within your field of interest,
- A clear understanding of the research gap in knowledge that will help to motivate your PhD research questions.
When assessing the academic papers or books that you’ve come across, you must think about the strengths and weaknesses of them; what was novel about their work and what were the limitations? Are different sources of relevant literature coming to similar conclusions and complementing each other, or are you seeing different outcomes on the same topic by different researchers?
When Should I Write My Literature Review?
In the structure of your PhD thesis, your literature review is effectively your first main chapter. It’s at the start of your thesis and should, therefore, be a task you perform at the start of your research. After all, you need to have reviewed the literature to work out how your research can contribute novel findings to your area of research. Sometimes, however, in particular when you apply for a PhD project with a pre-defined research title and research questions, your supervisor may already know where the gaps in knowledge are.
You may be tempted to skip the literature review and dive straight into tackling the set questions (then completing the review at the end before thesis submission) but we strongly advise against this. Whilst your supervisor will be very familiar with the area, you as a doctoral student will not be and so it is essential that you gain this understanding before getting into the research.
How Long Should the Literature Review Be?
As your literature review will be one of your main thesis chapters, it needs to be a substantial body of work. It’s not a good strategy to have a thesis writing process here based on a specific word count, but know that most reviews are typically between 6,000 and 12,000 words. The length will depend on how much relevant material has previously been published in your field.
A point to remember though is that the review needs to be easy to read and avoid being filled with unnecessary information; in your search of selected literature, consider filtering out publications that don’t appear to add anything novel to the discussion – this might be useful in fields with hundreds of papers.
How Do I Write the Literature Review?
Before you start writing your literature review, you need to be clear on the topic you are researching.
1. Evaluating and Selecting the Publications
After completing your literature search and downloading all the papers you find, you may find that you have a lot of papers to read through! You may find that you have so many papers that it’s unreasonable to read through all of them in their entirety, so you need to find a way to understand what they’re about and decide if they’re important quickly.
A good starting point is to read the abstract of the paper to gauge if it is useful and, as you do so, consider the following questions in your mind:
- What was the overarching aim of the paper?
- What was the methodology used by the authors?
- Was this an experimental study or was this more theoretical in its approach?
- What were the results and what did the authors conclude in their paper?
- How does the data presented in this paper relate to other publications within this field?
- Does it add new knowledge, does it raise more questions or does it confirm what is already known in your field? What is the key concept that the study described?
- What are the strengths and weaknesses of this study, and in particular, what are the limitations?
2. Identifying Themes
To put together the structure of your literature review you need to identify the common themes that emerge from the collective papers and books that you have read. Key things to think about are:
- Are there common methodologies different authors have used or have these changed over time?
- Do the research questions change over time or are the key question’s still unanswered?
- Is there general agreement between different research groups in the main results and outcomes, or do different authors provide differing points of view and different conclusions?
- What are the key papers in your field that have had the biggest impact on the research?
- Have different publications identified similar weaknesses or limitations or gaps in the knowledge that still need to be addressed?
Structuring and Writing Your Literature Review
There are several ways in which you can structure a literature review and this may depend on if, for example, your project is a science or non-science based PhD.
One approach may be to tell a story about how your research area has developed over time. You need to be careful here that you don’t just describe the different papers published in chronological order but that you discuss how different studies have motivated subsequent studies, how the knowledge has developed over time in your field, concluding with what is currently known, and what is currently not understood.
Alternatively, you may find from reading your papers that common themes emerge and it may be easier to develop your review around these, i.e. a thematic review. For example, if you are writing up about bridge design, you may structure the review around the themes of regulation, analysis, and sustainability.
As another approach, you might want to talk about the different research methodologies that have been used. You could then compare and contrast the results and ultimate conclusions that have been drawn from each.
As with all your chapters in your thesis, your literature review will be broken up into three key headings, with the basic structure being the introduction, the main body and conclusion. Within the main body, you will use several subheadings to separate out the topics depending on if you’re structuring it by the time period, the methods used or the common themes that have emerged.
The important thing to think about as you write your main body of text is to summarise the key takeaway messages from each research paper and how they come together to give one or more conclusions. Don’t just stop at summarising the papers though, instead continue on to give your analysis and your opinion on how these previous publications fit into the wider research field and where they have an impact. Emphasise the strengths of the studies you have evaluated also be clear on the limitations of previous work how these may have influenced the results and conclusions of the studies.
In your concluding paragraphs focus your discussion on how your critical evaluation of literature has helped you identify unanswered research questions and how you plan to address these in your PhD project. State the research problem you’re going to address and end with the overarching aim and key objectives of your work.
When writing at a graduate level, you have to take a critical approach when reading existing literature in your field to determine if and how it added value to existing knowledge. You may find that a large number of the papers on your reference list have the right academic context but are essentially saying the same thing. As a graduate student, you’ll need to take a methodological approach to work through this existing research to identify what is relevant literature and what is not.
You then need to go one step further to interpret and articulate the current state of what is known, based on existing theories, and where the research gaps are. It is these gaps in the literature that you will address in your own research project.