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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, to help identify specific limitations that should be mentioned in your manuscript it helps to consider these three categories separately to ensure you don’t miss anything.
How to Describe Your Limitations
Now that you know how to identify possible limitations in your study, the question turns to how to go about describing them in your article. In our experience, we’ve found that many authors are reluctant to write about their limitations because they feel it weakens their study and is pointing out flaws others may not have noticed. While this can make a person feel vulnerable, everyone knows that limitations are a part of science, and are looking for them anyways, so it’s better to be upfront about them. You can counter the reader’s presumed negative interpretation by providing them with an explanation for each limitation, showing 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. A statement to this effect could be declared in the limitations section of your manuscript, followed up by a comment about how the results might still be widely applicable as they will help with patient-specific treatment in all parts of the world.

If you have results that are particularly novel or you’re publishing in a little-researched field, another approach to supporting your findings in spite of limitations is to reinforce the novelty of your results. When breaking new ground, it is likely that there are still a lot of gaps in the knowledge base that need to be filled. Therefore, a good follow-up statement for this type of limitation is to describe what, based on these results, the next steps would be to build a stronger overall evidence base.

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.