Many authors are, understandably, reluctant to point out possible flaws or limitations inherent in their work. After all, isn’t that the point of peer review? However, discussing limitations will actually improve the overall quality of your manuscript as it shows that you have thought carefully about the positive and negative points associated with your research. Besides, many journals specifically request that authors include a section that discusses/acknowledges the limitation(s) of their study, so being able to do this is an important aspect of the writing/publication process.
Most authors will be aware that there are certain limitations to what they want to test or the possible outcomes achieved. The methods available within a particular laboratory or the specific characteristics of a study population may ultimately affect the results obtained.
Study limitations are often associated with design, statistics, and impact. Limitations due to restricted study populations or methodology are design limitations. In essence, you can only work with the tools available to you.
Statistical and data limitations may arise because the study population was too small (thereby under powering the study). This may be because you are studying a rare condition that not many people suffer from, or because few people were willing to take part in the study. Also, you may not have gathered as much useful data as you had hoped.
Impact limitations often arise because a study focusses on a very specific geographical region or population. This is a common limitation of studies conducted by Asian authors as they often focus solely on Asian populations. Such studies, although well designed and conducted, may not be “generalizable”. These three types of limitation often overlap, or one may give rise to another.
Once the limitations have been identified, they need to be described openly and honestly. Doing so should not be seen as denigrating your work. Indeed, they can be discussed in a positive light. For example, your results may be extremely novel, even if derived from a small and limited population. They may also be more widely applicable than they at first appear and so the next step may be to conduct a similar study in a more diverse population. These points can be emphasized to project the limitations in a positive light.
Open and frank discussion of study limitations should not be feared, it is part of the writing process and being self-critical is an important aspect of science writing. No study is perfect and all will have limitations. Simply put, identify the limitations and try to use them as a platform for improving your future work.