[For the previous post in this series on how to write a scientific paper, see here]
Time to wrap up the paper! You have presented your research question, its greater role in the universe, and your findings. Now let’s close the circle and discuss your answers and the questions that still remain, or the questions that you have just discovered. This is what the discussion section is for.
First, before we get started, a note for those poor souls who work in fields where you are not supposed to discuss your results in the Results section at all (see the previous Chapter). In this case, the Results section contains just data, and therefore the Discussion section usually has two parts, Discussion and General Discussion. The first part, Discussion, is about interpreting each of your results, which I have already covered in the previous chapter. The second part, General Discussion, is what we will mainly talk about in the following, and I’ll just refer to it with Discussion from now on. Sorry for the confusion (not my fault).
And while we are at it, what’s the difference between writing a Discussion or a Conclusion? The Conclusion is typically fairly short—it is almost like an echo of the abstract. It is a summary of what you have done, and it adds no new ideas or thoughts. In contrast, the Discussion section can introduce new points and insights (but of course no new results). It can connect the dots in new ways, and show how your findings relate to the broader issue at hand. It can ask new questions.
In the Discussion section, you should remind the reader of your research question and provide a synthesis of your results. You should present the answer to your research question and show how it contributes to solving the broader problem that you have painted in the abstract and the introduction. You should suggest further research based on your results. You should also contextualise your results (and your research problem) within the literature—this is a good opportunity to cite more papers that help to see where your results fit in and what they mean. It is quite common to cite in the Discussion section papers that were not cited in the Introduction: the Introduction and the Discussion are usually the sections of the paper that come with most citations.
There are several ways how to write the Discussion section, and there is a lot of freedom to choose the structure. One commonly used way is to begin by reminding the reader of the broader knowledge gap and the specific research question of the paper. You can then proceed through the results one by one, perhaps grouping them to make certain points and summing up all evidence before arriving at the final conclusion. Or, alternatively, you can begin writing the Discussion by recapping your question and your answer, the final conclusion of the paper. This is the inverted pyramid style, where you begin with the key points—the question and the answer—and then add in details and different points of view. These often appear in decreasing order of importance; however, even when using this approach, you should always have a strong ending (see below).
Whatever the structure you choose, a good Discussion section presents both answers and new questions. These new questions may be related, for example, to explaining your results—say, you have observed an effect that current theories cannot explain—or generalising them to other settings.
While it is common to discuss the limitations of your work in the Discussion section (leading to questions left for future research), it is in my view best not to mention limitations here for the first time. Let the reader know about them earlier. As I wrote in the chapter on Methods, all technical limitations should be discussed immediately when your methods are explained. You should also be open about what you can and what you cannot conclude from your results in the Results section (or the related bits of Discussion). Even though it is common to overgeneralise one’s results because everyone else does that too and the journals and the media like to have their headlines, please don’t. Be an honest scientist. It will pay off in the long run. You can also turn any generalisability issues into questions: instead of claiming that your observation is generally valid, ask if it can be replicated under different conditions or in different sets of data. You never know, one of your readers might pick up the question and do this.
The last paragraph of the Discussion section is very important. It contains the last words of your paper, your final words before back matter such as Acknowledgements—do not waste them. First, if the reader has been with you this far, reward her at the end. Think of a great pop song—even though the listener has heard the chorus already, the producer will always reward her with extra layers of intensity when the last chorus arrives. Do the same: at this point, the reader already knows the point of your paper, so add some icing on top, a new angle, or a new implication of your results. Second, endings are power positions. The last words of your paper will be remembered by your readers (or at least by those of them who made it this far and by those skimmers that directly jumped to the end). Never waste a power position, never waste an ending! Always end on a high note.
There are some all too common ways of ending with a whimper instead of a bang. One way is to focus on the limitations of your work in the final paragraph in a negative light, instead of turning them into a question (see above); in general, it’s better to discuss limitations much earlier than in the last paragraph. Another common problem is ending the paper with a vague statement like “further research is needed”. Further research is always needed, this just makes it sound like you didn’t do enough even when you did! Besides undermining the importance of your work, vague statements are never memorable. Say something that you would want the reader to remember.
One good way of ending the Discussion section—and the paper—is to write a short paragraph that recaps your conclusion and the significance of your work. You can even signpost this to the reader and begin the paragraph with the words “in conclusion, we have shown that…” This paragraph can resemble the bottom part of the hourglass of the abstract; it can also be written in the style of a news lede. What did you found out and why? What does it mean? What are its broader implications? How has your work concretely contributed to the big picture? Where have you come from where you started? How has the world now changed because of your results? This paragraph closes the circle and resonates with your Introduction.