There are only a few rules for writing a good abstract, but they are important and not easy to comply with. Before considering these rules, it is important to check the maximum number of words and required format, if any, you are expected to deliver.
How long should my abstract be?
As brief as possible. Remember what Einstein said: “You should explain everything as simply as possible, but not more so.” In other words, being brief may force you to limit what you say about an aspect of your study. Be careful not to make a point so brief that no one will understand it. If you find yourself forced to do so, better to jettison the point(s) allowing more space to the points that remain. Better to get one point across than to fail to get three points across. Chose the points for your abstract judiciously.
How much knowledge should I assume my audience has?
Although it is important to know who your audience is, in general, it is best to assume little knowledge. You will rarely get points for showing off how much you know if you don’t make your audience understand your work. This often requires simplifying your abstract to some extent (see Einstein above). Be careful that you don’t alter the facts in your abstract in the process of making it accessible to others.
Which parts of an abstract are especially important?
The two most important parts of an abstract are the title and the conclusions. These are important for two reasons: 1) they are often the only parts of an abstract that are read, and 2) they are often, therefore, the only chance you have of making clear what your abstract is about and getting people interested in your study.
What should I think about when thinking up a title?
Make it short and clear. Try to make the title say what your study was about and, if possible, what the major result was. Make the title interesting so that people will want to read on. Consider these three titles for the same study:
Treatment of eczema in children.
Probiotics in the treatment of eczema in childhood: a randomized controlled trial.
No effect of probiotics in the treatment of childhood eczema: a randomized controlled trial.
The first is boring and uninformative. The second is much more informative than the first, but the third is the best because it also tells the reader what to expect. And readers like knowing what to expect.
What is important in the conclusion?
The conclusion should state not just what you found in your study, but also what it means. Remember that most readers will, if your title has peaked their interest, read the conclusion next. Be very careful not to conclude more than your results allow, but formulate your conclusions in a way that places your findings in a context your audience will appreciate. Don’t simply state that your results are interesting or important, but explain why they are so. Be enthusiastic but don’t overstate your case.
If you have got your audience to the point that they are reading on after the conclusions, you are doing well! State clearly in the Introduction or Background why the study was done and why this study is important. Whether or not you include a separate Aim, state clearly what the aim of your study was. Be specific. Getting your question right makes the rest of the abstract easy going for the reader. Leaving it vague makes the reader stumble around wondering where he or she is going. In the Methods, make sure to explain what was compared with what. In the Results, avoid hanging comparisons:
NOT: children treated with probiotics had lower eczema scores at the end of the study
The reader will ask: lower than who or what?
BUT: children treated with probiotics had lower eczema scores at the end of the study than those treated with placebo
Find someone unfamiliar with your work and have them read your abstract. It will help you identify confusing passages for which you have become “blind”.