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How to Write About the Limitations of a Scientific Study

Lmitations 1

You’ve analyzed your results and reached some conclusions. Now, you’re ready to tell the world about what you’ve found and convince editors, peer reviewers, and readers that it’s important. So how do you tackle the task of also telling them about the limitations of your work?

How to write about the limitations of a study

No study is perfect, no matter how elegant its design may be, and many journals require authors to write a section at the end of the discussion about the limitations of their study. For some studies, these limitations will be obvious: small sample size, multiple comparisons without corrections, observational design and risk for confounding. For other designs, the limitations may be less obvious, but you’ll still need to list them.

Six tips for writing your limitations section

  1. Focus on weaknesses in your design and analyses, rather than results.
  2. Start with a bold statement: “This study has some limitations.” Don’t try to soften it with less obvious language.
  3. Enumerate the limitations, if you can. If you have three limitations to discuss, say so: “This study has three main limitations.”
  4. Be direct about what they are. “The first limitation is the small number of participants.”
  5. Explain if needed, but without being defensive. “Because this condition is so rare, we anticipated that recruitment might not meet targets. However, also because the condition is rare, the findings of this study offer new, potentially useful information for this patient population.”
  6. Signal that you are wrapping up your limitations: “Finally, we could not control for every possible lifestyle factor, and the observational nature of this design leaves the possibility of residual confounding.”

What not to include in the limitations section

You do not need to include every single thing that you personally view as a limitation of the work. For example, if you were late in making a measurement one day, but that timing did not affect outcomes, you probably don’t need to mention it.

Do not be extremely defensive. Don’t expend a lot of language explaining why your work had the limitation. See above for an example of how to explain a limitation while still emphasizing the importance of your work.

Usually, avoid pointing fingers in an accusatory way at other studies. If your work has a specific limitation because of real-world considerations, you can point that out, rather than saying as justification that some other author group or groups did the same thing.

In a similar vein, the limitations section is not usually the place to compare a limitation of your study favorably to the limitations of other studies. For example, you should not say, “We had only 25 participants, but Smith et al. had only 12 and they still published their results.” That comes across as defensive and uncollegial.

Where do you comment on the strengths?

The usual practice is to place the strengths of a study ahead of the limitations. Most authors will list the strengths, beginning with a phrase such as, “Our study had several strengths,” and then briefly describing what those are. As with limitations, these strengths usually will relate to design: large population, excellent controls, multiple adjustments, or double-blind design. If your design is considered more stringent than what others have used before (e.g., a randomized trial as opposed to an observational study), that’s a particular strength. When you’ve listed your strengths, then you move to your limitations, using phrasing such as, “Our study also had some limitations.”

Acknowledging a study’s limitations is an important part of the process of science and of communicating your results. It shows that you are willing to mention and discuss the weaknesses as well as the strengths of your work and suggests an intellectually honest presentation of your findings.

 

San Francisco Edit specializes in scientific editing in the United States and we work with scientists from all over the world.

 

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