Writing a Good Comparison Sentence

It is often necessary to compare two or more items in academic writing, especially in the sciences. Comparisons can provide useful information and create a framework for understanding some results in the context of others. However, comparisons also create the opportunity to confuse the reader with imprecise or ambiguous wording. Given the importance of accurately and concisely conveying your results, what is the best way to write a comparison sentence?

The most critical aspect of any comparison is parallel structure. That is, each item being compared should be from the same type of thing. (In English, we say not to compare apples to oranges.) Consider the following example:

• The asteroid belt is approximately 1,000 times farther from the Sun than the Earth and Moon.

The current structure of this sentence makes it sound as though the distance from the asteroid belt to the Sun is being compared to the distance between the Sun and the Earth and Moon. However, this interpretation is incorrect (the asteroid belt is only 2 to 3 times as far from the Sun as the Earth or Moon is).

Instead, consider "The asteroid belt is approximately 1,000 times farther from the Sun than the Earth is from the Moon." Now, the distance between the first two items mentioned is being compared to the distance between the next two items.

• Treatment with Compound A generated more muscle regrowth than Compound B.

This sentence compares treatment with Compound A directly to Compound B, instead of focusing on the effects of treatment with Compound B. Instead, try "Treatment with Compound A generated more muscle regrowth than treatment with Compound B."

Many comparisons are written incorrectly to save space, as extra words are often necessary to achieve proper parallel structure. One common way to reduce the number of additional words in a comparison is the use of demonstrative pronouns (e.g., 'that' or 'those'). Consider the following examples:

• The growth rate of Mycobacterium smegmatis is faster than Mycobacterium tuberculosis.

Currently, this sentences compares a growth rate to a species of bacterium.

Instead, consider "The growth rate of Mycobacterium smegmatis is faster than that of Mycobacterium tuberculosis." or simply "Mycobacterium smegmatis grows faster than Mycobacterium tuberculosis."

• The bond length of dioxygen is similar to carbon monoxide.

Here, the bond length of one molecule is being compared to another molecule instead of its bonds.

A better version could read: "The bond length of dioxygen is similar to that of carbon monoxide."

• The colors used in Henri Matisse's paintings are similar to those of Andre Derain.

The colors in Matisse's paintings should be compared to colors in other paintings, not the colors of a painter (which could be considered to describe his appearance, not his work).

Another way to write this sentence is "The colors used in Henri Matisse's paintings are similar to those used in Andre Derain's paintings."

We hope that this information will help you the next time you have to make a comparison in your writing! If you have questions about writing a strong comparison, please write to us, and we'd be happy to assist you.