When writing manuscripts for publication, there are many important details that need to be included to present a well-balanced, comprehensive description of your work. One of the most important but often underrated of these details is the limitations section of your manuscript. While you may be reluctant to discuss any flaws of your study, it’s important to provide accurate context for your work and give readers sufficient information to properly evaluate the relevance and impact of your results. Also, because everyone knows that limitations are a part of science, and are usually already looking for them, it’s better to be upfront.
So, what’s the best way to go about describing limitations without invalidating your findings? Let’s approach our strategy in a methodical way by first looking at the types of limitations you might encounter.
Types of Limitations
Before you even start your study, you may be aware that there are certain limitations to what you want to test or what possible results may come of your efforts. The procedures you have available or specific constraints on the study population may ultimately affect what outcomes you can obtain. These we can refer to as study design limitations.
Another type of limitation to consider is what we might call an impact limitation. Even if your study has strong design and excellent statistics, it can suffer from limited impact from factors such as a strong regional focus, being too population-specific, or the field being only conducive to incremental findings.
A final type of limitation is that of statistical or data limitations. Sometimes you may not be able to collect as much or as good data as you intended, or perhaps enrollment was more difficult than expected, underpowering your results. Statistical limitations can also stem from study design, producing more serious limitations in terms of interpreting the findings.
Although these three types of limitations are often connected, it helps to consider these three categories separately to ensure you don’t miss anything.
Where to Put the Limitations
Generally, the limitations are placed near the end of the discussion. Most authors include the limitations as a separate paragraph, usually starting with a lead sentence such as “However, our study had several limitations”. Alternatively, you can work the limitations into relevant sections of the general discussion.
For example: If you are already discussing how your results compare with those from a previous study conducted in another region/country, you could include any study limitations associated with a restricted sampling area or study population.
Structuring Your Limitations
Once you have decided what your study limitations are and where you want to include them in your manuscript, it’s just a matter of framing each one in the most positive light. The easiest way to approach this is to briefly state the limitation and then discuss why your results are still relevant, addressing each limitation in turn. This also applies if you are working your limitations into the rest of the discussion.
If you counter the reader’s presumed negative interpretation by providing them with an explanation for each limitation, you will show them why the results are still important.
For example: Your study looked at the efficacy of a new diabetes treatment in Japanese patients. The results were very positive; however, because you only looked at Japanese patients, these findings may not translate to patients of other ethnicities. After making a statement to this effect, you could discuss how the results might still be widely applicable in helping with patient-specific treatment in all parts of the world.
One of the best ways to do this is to suggest directions for future research.
For example: If you only collected samples from one or two provinces in China, you could suggest that future work include samples from a greater geographic area or be expanded to a multi-country analysis. This way, your work remains relevant because it is clearly the foundation for future studies. Alternatively, you could say that your findings contribute to the emerging global picture of disease and form the basis for future, more integrated studies. This would also be appropriate if your work was incremental in nature.
Now, it is possible that your study will have a fairly critical flaw (usually in the study design) that decreases confidence in your findings. In this case, it will probably also be apparent to others, so it’s best to explain why this error or flaw occurred. You can still explain why the study is worth repeating or how you plan to re-test the phenomenon, but it is also likely that your publication goals may need to be lowered if you still plan to publish your work.
Finish on a Positive Note
The limitations don’t need to be extensive; one sentence stating each limitation and then one or two sentences explaining and mitigating each limitation is fine. Most importantly, readers should leave with a positive overall impression of your work. To do this, we recommend moving immediately from discussing the limitations to providing the final summary of your study. Whether this is a separate “Summary” section or the last paragraph of the discussion, there is no need to include any further discussion of the limitations—this section is your chance to reiterate the importance and applications of your research.
Limit Your Expectations
No one expects science to be perfect the first time and while your peers can be highly critical, no one’s work is beyond limitations. Our knowledge base is built on uncovering each piece of the puzzle, one at a time, and limitations show us where new efforts need to be made. So much like peer review, don’t think of limitations as being inherently bad, but more an opportunity for a new challenge. In the end, your limitation may be someone else’s inspiration.