How to write a clear comparison sentence
Let's talk about comparisons.
Comparisons, or comparative sentences, are a blind spot for many academic writers, but especially those for whom English is not a native language.1
How a comparison sentence can go wrong
It goes wrong when writers just stick the words "compared to" in the sentence and leave it otherwise unchanged.
Compared to Method A, Method B is safe.
But this is not a comparison sentence!
This sentence only tells me that Method B is safe. I don't know how Method B relates to Method A. Was Method A less safe? Was it not safe at all?
The number of peptide A increased compared to the number of peptide B.
This sentence only tells me that the number of peptide A increased. I don't know what happened to peptide B. Did it increase as well, but not as much? Did it not change at all?
How to write a clear comparison sentence
To write a clear comparison sentence, take the time to think through how the parts of your research actually relate to each other and then use a clear verb to show that relationship.
If the relationship is not clear in your mind, you won't be able to put it clearly down on paper. Use the steps below to force yourself into a clear structure.
1. Figure out which situation you are in
Decide whether you are comparing how two things look at one moment in time or how two things changed over time. Neither situation needs the word "compare":
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One moment in time (an end result): The signals in A were twice as high as the signals in B.
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A. Change over time (both things changed, but one changed more than the other): The signals in A increased twice as much as the signals in B.
B. Change over time (one thing changed but the other did not): The signals in A doubled, while the signals in B stayed the same.
2. Use parallelism
Comparisons require parallelism, so lay out the groups and the differences between them in parallel structure. You cannot compare apples and oranges. Go as far as to line up each parallel part on top of each other to help you see the relationship:
Surgery is recommended for high-risk patients, while
therapy is recommended for low-risk patients.
3. Use "than"
Less experienced writers often think they have to use the word "compare" in a comparison ("in comparison with" and "compared to/with") and they often end up with a relationship that is at best vague and at worst nonsensical. Most of the time you can avoid the word "compare"2 completely because is it unnecessary and wordy.
Don't use the word compare by default. Show the comparison using than.3
If you are comparing within a single phrase, there are a few basic comparison structures, all of which use than:4
A is more/less/higher ... than B.
A has a more/less/higher ... than B.
More/fewer people did A than B.
A occurred more/less often than B.
4. Use precise, consistent verbs and adjectives
The key to writing a clear comparison sentence is to think carefully about how the groups relate to each other and to make that relationship explicit.
Verbs are the lifeblood of sentences--they show us the relationship between two nouns. In a comparison, a verb, adjective, or adverb can often show a relationship more clearly than a noun.
Use verbs, adjectives, and than instead
These broader criteria are justified
These broader criteria are justified because biotherapeutics are more complex than small molecules.
If the relationship is the same in both groups, don't use a synonym, use the same verb or adjective!
Method A is favorable, while Method B is desirable.
Methods A and B are both advantageous.
5. Put the comparison phrase in between the groups that are compared
The simplest structure to offer a reader is subject-verb-object (SVO). Follow this structure whenever possible in comparisons.
Group 1 - Comparative - Group 2.
Method A is faster than Method B.
Comparative - Group 1 - Group 2 - Comparative.
Compared to Method B, Method A is faster.
You might be thinking:
But if I was just talking about Method B, then I want to put Method B in the beginning of the sentence, so what is actually wrong with that sentence?
It is not ideal to break up SVO structure because a verb shows a clear relationship between two nouns: the comparison relationship5. You can put Method B in front and still keep SVO structure:
Method B is slower than Method A.
Here are two more examples that show why you need to keep the comparison relationship together.
In this sentence, I have to read all the way to the end before I find out what the two comparison groups are:
Free light chains have a shorter half-life (than what?), which allows them to more accurately assess immune activation
Free light chains have a shorter half-life than serum Igs, which allows them to more accurately assess immune activation.
This sentence is missing a comparison group:
Serum FLC (κ and/or λ) concentrations are higher
Serum FLC (κ and/or λ) concentrations are higher in group A than in healthy controls.
Challenge yourself to write a crystal clear comparison sentence in your next article! Good luck!
Footnotes
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Smart, capable (mostly non-native English speaker) academics regularly struggle to make clear comparison sentences. I'm even talking tenured professors here (!) However, most academics don't even realize their comparison is not clear until someone points it out to them. I'd like to see more results presented unambiguously, hence this post. ↩
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And all its forms: compare, compares, comparison, compared. An added benefit to removing "compare" is that you no longer have to wonder which preposition to use: "compared to?" "compared with?" Who cares? Just use "than!" ↩
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Sure, in certain cases you can make an exception here, but in the vast majority of cases this rule applies. ↩
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Replace the adjective in italics to fit your relationship. ↩
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Sometimes you will. This is not a hard and fast rule. Most of the time you should try to keep the comparison together. ↩