First to be read, last to be written
Your paper’s abstract is critical because many researchers and journal editors will read only that part. Your abstract should provide an accurate and sufficiently detailed summary of your work so that readers will understand what you did, why you did it, what your findings are, and why your findings are useful and important. Your abstract must be able to stand alone as an overview of your study that can be understood without reading the entire text. However, your abstract should not be overly detailed. For example, it does not need to include a detailed methods section.
Even though the abstract is one of the first parts of your paper, it should be written last. You should write it soon after finishing the other sections, while the rest of the manuscript is fresh in your mind. Requirements for abstracts differ among journals, so the target journal’s instructions for authors should be consulted for specific details.
Specific journal requirements
Despite differences among journals, there are a few general rules that should be obeyed when writing an abstract:
The word limit should be observed. 250 words is probably about average and is a commonly adopted word limit. Technical jargon should be avoided, although what is considered “technical” may vary depending on the target journal’s audience. If technical terminology is unavoidable, it should be defined in simple terms when first used.
Abbreviations should be limited. Their acceptability depends on your target journal. For example, HIV is likely to be acceptable in abbreviated form by most journals. By contrast, even though RT-PCR might be acceptable in a journal reporting molecular biology techniques, even here it would need to be spelled out in full at first use. Abbreviations used three or more times should be defined at first use. However, abbreviations used only once or twice should be spelled out in full unless doing so causes the word limit to be exceeded. Many journals provide a list of acceptable abbreviations on their websites. Abbreviations that are defined in the abstract will need to be defined again at first use in the main text. Most journals do not allow references to be cited in the abstract. Always read a journal’s instructions to authors. Even if you have submitted to a journal before read the instructions again – they might have been altered.
Structured or unstructured abstract
Some journals request structured abstracts divided into sections such as background, objectives, methods, results, and conclusions. Clinical journals may require additional or alternative sections, such as Patients, Interventions or Outcomes. Always check your target journal’s instructions for authors to determine the particular formatting/outline requirements prior to writing your abstract.
Abstracts are usually followed by a list of keywords selected by the author. The instructions for authors will state how many keywords are required and may even provide a list of recommended keywords. Choosing appropriate keywords is important, because these are used for indexing purposes. Well-chosen keywords enable your manuscript to be more easily identified and cited. Always check your target journal’s instructions for authors as often journals will specify that terms used in the title of your paper should not be used as keywords. For clinical papers, keywords may need to be chosen from the Medical Subject Headings list