Compare with care

Scientific research papers are filled with comparisons – for example, test variables are compared with controls or treatment groups are compared with placebo groups. Ideally, the reader should be able to understand which variables are being compared and what the difference between them is. For this, the comparison needs to be clear and logical, but scientists often struggle with this. In this post, I give useful tips for writing effective comparisons.

Sentences making comparisons are often filled with information (group names, variables, values, statistics, etc.) and it is often difficult to decipher what is being compared. Putting the things that are being compared close together often helps with this. Let’s take a look at some examples. Consider this title for a research paper:

Trial sequential analysis of the effect of melatonin on postoperative sleep quality measured with visual analogue scale in adults compared with placebo

The problem with this comparison is that the two things being compared (melatonin and placebo) are separated by intervening information. That makes it harder for the reader to figure out exactly what is being compared. The solution is simple – put them together:

Trial sequential analysis comparing the effects of melatonin and placebo on postoperative sleep quality measured with visual analogue scale in adults

Now consider this sentence from a Results section:

Among six observational studies, three found Hispanic patients were less likely to receive labour epidural analgesia compared with non-Hispanic White patients (adjusted odd ratio [aOR] range, 0.44 to 0.80) after adjusting for covariates.

The reader needs to work to figure out what is being compared here. Putting the two things being compared (Hispanic patients and non-Hispanic patients) together in the sentence helps the reader out:

Among six observational studies, three found Hispanic patients were less likely than non-Hispanic White patients to receive labour epidural analgesia (adjusted odd ratio [aOR] range, 0.44 to 0.80) after adjusting for covariates.

To help you identify this problem in your own paper, underline the things you are comparing in your sentences. If they are separated, put them together!

Leaving out crucial information is a common problem in research writing. It usually happens because the writer knows their own thoughts so well, they assume that the reader knows what they are talking about. Or they assume that because they have mentioned it earlier in the paper they do not need to mention it again. But repeating the information often helps the reader to understand the point being made. In sentences making comparisons, a common mistake is leaving out one of the things being compared. Consider this sentence:

Larger than what? This sentence only mentions one variable (the partially edentulous model), so it is not clear what they are comparing this with. Although the models are probably explained in detail elsewhere in the paper, both things being compared need to be specified in this sentence to avoid confusing the reader.

Compared to and compared with have different meanings but are often used interchangeably in research papers. So what is the difference? Compared to shows that two things are similar whereas compared with points out similarities and differences between two things. In most cases, compared with is the correct choice in a scientific research paper because we are usually looking for differences between variables; we rarely want to make the statement that two things are similar.

Comparisons are more effective if we specify what the difference is between two variables rather than just saying there is a difference. For this, we use comparative adjectives like higher and lower to tell our reader exactly how two variables differ. These comparisons are clearer if we use than after the comparative adjective instead of compared with. For example:

The Injury Severity Score was larger in group A compared with group B (Incorrect)

The Injury Severity Score was larger in group A than in group B (Correct)

Also take care not to use more with comparative adjectives or most with superlative adjectives:

The patient number was more higher in group A than group B (Incorrect)

The patient number was most highest in group A (Incorrect)

Comparisons are unavoidable in research writing. They form a crucial component of our interpretations and argumentation. Following the tips outlined in this post will help you to write clear and effective comparisons in your next research paper.

Claire Bacon is a former research scientist with professional qualifications in copyediting and medical editing. She edits scientific research papers and teaches courses on scientific writing.