When we set up an experiment, we often have more than one group, perhaps a control group and an experimental group; for example, healthy individuals vs. patients with diabetes, untreated cells vs. cells treated with a tyrosine kinase inhibitor, or regular plants vs. transgenic plants. We may even have multiple experimental groups. Today we discuss a few things authors should pay attention to when making statements involving comparisons.
1. Make sure to indicate the items being compared.
Tumor cells treated with compound A showed lower expression of Bcl2. (incorrect)
Tumor cells treated with compound A showed lower expression of Bcl2 than vehicle control-treated cells. (correct)
When a comparative adjective or adverb is used, readers will expect to see a comparison between two items, so the items being compared should both be mentioned in the sentence. In the above example, the word “lower” indicates a comparison is made, and we need to be clear that two types of cells are compared.
Our proposed algorithm is a more robust and accurate method for predicting erosion in pipelines. (incorrect)
Our proposed algorithm is more robust and accurate for predicting erosion in pipelines than existing algorithms. (correct)
Our proposed algorithm is a robust and accurate method for predicting erosion in pipelines. (correct)
In this example, if we use “more robust and accurate,” we need to say what is compared with our algorithm. Alternatively, removing the word “more” makes the sentence grammatically correct. As a conclusion of the study, we may only want to say that our method is robust and accurate.
A better understanding of the pathogenesis of muscular dystrophy may lead to novel therapies. (acceptable)
Occasionally we see sentences like the example above in manuscripts. The sentence here does not explicitly indicate the two items being compared because it is understood that the authors mean an understanding better than what we currently know about the pathogenesis of the disease. Such sentences should be used sparingly in a manuscript and never be used to describe specific experimental results.
2. Make sure the items are comparable
We can only compare things of the same type. In the examples above, cells are compared with other cells, and an algorithm is compared with other algorithms. In our experiments, we of course only compare things of the same type, but if we are not careful when we write up the results, readers may get confused regarding what is compared with what.
The 1000-grain weight of rice treated with fertilizer A was higher than fertilizer B. (incorrect)
The 1000-grain weight of rice treated with fertilizer A was higher than rice treated with fertilizer B. (incorrect)
The 1000-grain weight of rice treated with fertilizer A was higher than that of rice treated with fertilizer B. (correct)
Rice treated with fertilizer A had a higher 1000-grain weight than rice treated with fertilizer B. (correct)
In this example, the 1000-grain weight is being compared, but in the two incorrectly written sentences, it is compared with either a fertilizer or rice. One way to solve the problem is to add “that of” in the sentence. We can also restructure the sentence as shown in the last sentence of the example.
Notice that I have used “than” in these examples. You can also use “compared with” but “than” is preferred by native speakers. However, in some sentences, “compared with” should be used.
Compared with the Beijing-Tianjin-Heibei region, the Yangzi River Delta region had higher annual average precipitation. (“Than” cannot be used here to replace “compared with”)
The Yangzi River Delta region had higher annual average precipitation than the Beijing-Tianjin-Heibei region. (The sentence is restructured to use “than”)
The annual average precipitation was higher in the Yangzi River Delta region than in the Beijing-Tianjin-Heibei region. (Another way to write this sentence)
The annual average precipitation in the Yangzi River Delta region was higher than that in the Beijing-Tianjin-Heibei region. (Yet another way to write this sentence)
These four sentences are all acceptable and express the same meaning. The shortest sentence, which is the second one, is usually the best, but you might use other forms to better fit the flow of the paper.
3. Use different words for changes over time and differences between groups
Words such as “increase” and “decrease” describe a trend and thus imply changes in the same sample over time. To describe differences between distinct groups, words such as “greater,” “larger,” “lower,” “smaller,” and “shorter” should be used. Imagine we have a study where patients with low hematocrit received two different treatments, and hematocrit levels were measured in the two groups of patients before and at different time points after the treatments. When describing the results, it is necessary to be clear whether we mean changes in the same group or differences between the two groups.
Hematocrit levels increased in both groups following the treatments and peaked at 1 week post-treatment in group A but peaked at 3 weeks post-treatment in group B. (Here we describe the trend in each group)
At the 3-month post-treatment follow-up, patients in group A had higher hematocrit levels than those in group B. (Here we describe a between-group comparison)
If you only have two groups but have no changes over time, avoid using “increase” or “decrease.” However, the results may suggest a trend of increase or decrease.
ELISA showed that fibroblasts treated with the inhibitor secreted more CCN2 into the culture medium than untreated cells.
These results suggest that this inhibitor increased CCN2 secretion in fibroblasts.
(Please retain the reference in reprint: http://www.letpub.com/index.php?page=author_education_Describing_comparisons_in_a_manuscript)