Writing a cumulative dissertation

2019-10-21

A cumulative dissertation is a collection of articles which have been published in recognised scientific journals or accepted for publication. My PhD dissertation is a cumulative one and in this blog post I describe its structure and things to pay attention to when writing your own.

Identify articles and contributions

Identify the articles that make up your dissertation and identify the main contributions of these articles. A single article can have multiple contributions and a single contribution can be explored in multiple articles.

For example, consider the following articles with their corresponding contributions:

Article Contribution
How to better harvest bananas Banana harvesting method
Discovery of a brown magic powder Cacao powder
What do almonds and butter have in common? Almond butter
1, 2, 3, brownies! 3-Ingredient brownies

The first three contributions (ingredients) are used in the fourth and final contribution (recipe).

Structure

The structure of your dissertation looks as follows (in chapters):

  1. Introduction
  2. Chapter about contribution 1
  3. Chapter about contribution 2
  4. ...
  5. Conclusion

Chapter 1 provides an introduction to the work that is described in chapters 2 and onwards. Chapters 2 until the second to last align with the articles/contributions. The final chapter concludes the dissertation and looks beyond the work conducted during the PhD.

Considering that we have four articles/contributions in our example, its structure looks like this:

  1. Introduction
  2. How to better harvest bananas
  3. Discovery of a brown magic powder
  4. What do almonds and butter have in common?
  5. 3-Ingredient brownies
  6. Conclusion

Note that the titles of the chapters do not necessarily need to be the same as the title of the articles. They can be altered if it better fits the story.

For example

  1. Introduction
  2. Ingredient: bananas
  3. Ingredient: cacao powder
  4. Ingredient: almond butter
  5. Recipe: 3-Ingredient brownies
  6. Conclusion

Introduction chapter

Or "the story of your PhD".

The introduction chapter is similar to an introduction section in an article. This chapter is the most important one as it describes the problems the dissertation tackles, what the contributions are, and how the contributions are related to each other. This last one is really important as it turns everything in a single, coherent story! Consequently, you will spend the most time on this chapter.

The chapter includes the following parts:

  1. General introduction to the problem space.
  2. More detailed introduction to a part of the problem space.
  3. Challenges that are tackled in the dissertation.
  4. Background information needed to understand the research questions and hypotheses.
  5. Research questions and hypotheses based on the challenges, together with the corresponding contributions.
  6. List of publications.

Try to make parts 1 - 3 as understandable as possible for people who are not part of your academic community, such as family, friends, colleagues from other departments, and so on. I highly recommend to start using an example as early as possible and make that example related to something that everybody understands.

Parts 4 and 5 should still be as understandable as possible. Of course, here it's hard to avoid all technicalities because you have to get to the essence of your dissertation at some point. But at least try.

Some of your articles might have a research question. If that is the case: nice, you can reuse them! But check if they need rephrasing to fit your story. If you have articles without a research question, create one that both fits the story and the work described in the article. Ideally, every research question should also have an hypothesis, which might already be in the original article or that is newly created for the dissertation. Note that not every research question needs an hypothesis. In my case I had a more exploratory article without a research question. I created a research question, but not a hypothesis because that did not make sense. This all depends on the article itself. So check your articles and your story, and see what is possible and what is not.

Part 6 contains two lists: one list with the main articles of the dissertation and a list with all publications you (co-)authored during your PhD.

In general, make sure that you have story (not just a bunch of words and paragraphs) that is clear, not too technical, but still positions and outlines the great contributions of your dissertation.

Aligning this with our example results in

  1. General introduction to cooking and desserts.
  2. More detailed introduction to creating cake-like desserts with a limited amounts of ingredients.
  3. Challenges are
    • Improve the efficiency of bananas in desserts,
    • Find an alternative way to flavor a cake-like dessert,
    • Find an alternative butter that works in desserts, and
    • Create a cake-like dessert that has at most four ingredients.
  4. Background information about desserts, recipes, ingredients, and so on.
  5. Research questions and contributions are:
    • "How to improve the harvesting of bananas?" with as contribution a new method,
    • "How to flavor desserts through the use of powder?" with as contribution cacao powder,
    • "How to improve the consistency of desserts through a non-conventional ingredient?" with as contribution almond butter, and
    • "How to create a cake-like dessert using bananas, cacao powder, and almond butter?" with as contribution: 3-ingredient brownies.
  6. List of publications.

Contribution chapters

Ideally every contribution is contained in a single article and you can put every article in a separate chapter. That way a single research question and hypothesis is aligned with a single chapter. If it reads better (for the story) to put multiple articles in the same chapter, then that is not a problem. Looking at our example we could have something like

  1. Introduction
  2. Ingredients: bananas, cacao power, and almond butter
  3. Recipe: 3-Ingredient brownies
  4. Conclusion

This is fine. Important to note here is that this all depends on the story you set out in the introduction chapter. So I suggest to create a decent version of that chapter first before moving on to the contribution chapters.

The structure of a contribution chapter is as follows

  1. Introduction
  2. A copy of the original article

The introduction includes how the chapter fits into the story, where in the story the reader is, and what is discussed. Note that the content of the original article can be adjusted, for example, to

  • Rephrase the research questions and hypotheses.
  • Replace words to make them the same across all articles, because you might use different words for the same concept across different articles. It happens to all of us, especially when there are four years between the first and last article.

Conclusion chapter

The conclusion chapter is similar to a conclusion section in an article. It concludes your story and looks at what can be investigated in the future. More specific, its structure is as follows

  1. Impact of contributions
  2. Remaining challenges and future directions

The first part reflects on the research questions, hypotheses, and corresponding contributions, and discusses how they tackle the challenges mentioned in the introduction chapter. The second part describes remaining challenges based on aforementioned challenges and contributions.

Remaining challenges for our example are

  • How to create similar brownies with different flavors?
  • The production of almond butter needs to be improved if its used in more and more recipes.

Additionally, the second part also discusses future directions:

  • What we can do next to tackle these new challenges.
  • What was already done by you regarding these challenges. This is not needed, but do mention it if have you done something.
  • What your vision is for the future.

For example

  • Can we change the flavor of cacao powder to change the whole flavor of the brownies?
  • Higher quality almond butter can be produced through the use of dedicated fridge as described in my most recent article.
  • In the future more and more recipes will rely on almond butter, both from an economic and flavor point of view.

Conclusion

These are the most important things that I have learned during the writing of my dissertation. Note that these are mere suggestions that might or might not work for your dissertation, so do not hesitate to deviate from them if you feel the need to. It is your story after all 😉

Good luck!

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If you have any questions or remarks, don’t hesitate to contact me via email or via Twitter.