The word “respectively” can be useful in scientific writing to clarify relationships between several different words in a sentence. It’s used to indicate to the reader that the relationship between two sets of words or phrases can be read in terms of the order in which they appear.

Huh?

It might be easier to explain with an example. In this case, I’ll use colors to show you the relationships that are implied between two sets of nouns when you use the word “respectively” at the end of a sentence.

Example: “The peak absorption wavelengths of samples A and B were 710 nm and 600 nm, respectively.”

So in this sentence, we have a set of samples (A and B) and a set of numbers (710 nm and 600 nm). The word “respectively” tells the reader that the samples and numbers that correspond to one another occur in the same order in which they appear. So the first value (710 nm) corresponds to the first sample (A). Likewise, the second value listed in the sentence (600 nm) corresponds the second sample (B).

Let’s do another example.

Example: “The dog and the cat were named Jack and Sam, respectively.”

So what is the dog’s name? And what's the cat’s name?

Since the dog is listed first in the sentence, the word “respectively” lets you know that the dog’s name also corresponds to the first name that’s written (Jack). And since the cat is listed second, its name would be the second name listed in the sentence (Sam).

A note on punctuation: the word "respectively" is put at the end of the sentence or phrase it refers to, and it is set off with a comma (or commas if "respectively" occurs in the middle of the sentence).

Example: The dog and the cat were named Jack and Sam, respectively, and they lived down the street from me.
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If you have any doubts about how to use “respectively” in a sentence, I suggest you avoid using it so you don’t unintentionally confuse the reader. It can be a useful writing tool, but it's often not necessary. The sentence can usually be re-written in another way to express the same information.

If you would like to learn more writing tips and tricks, check out my PowerPoint presentation An Introduction to Writing in Science, available in ebook format on the Amazon Kindle app. 

Acronyms are a type of abbreviation that are typically constructed from the first letters of the individual words in a phrase.

Example: single-walled carbon nanotube = SWCNT
(I’ve underlined the letters for emphasis only)

These abbreviations can also include letters from inside the word (as in nanotube), particularly when that word could be broken down into two individual parts that have meaning on their own (e.g., nano and tube).  

Acronyms can be useful in science so you don’t have to repeat long phrases like “single-walled carbon nanotubes” 50 times throughout a manuscript. However, you should follow these rules if you’re going to use them in your writing:

1) USE ACRONYMS SPARINGLY

Many scientists have a tendency to over-use acronyms, possibly because they believe that shortening phrases will make the work easier and faster to read, but this couldn’t be further from the truth.

The issue is that acronyms are essentially a code – they stand for some other idea. But readers have a hard time keeping track of multiple codes. If they forget what your acronym stands for, they’ll have to go back to where it was first defined in the paper, which is time-consuming and annoying. Or (and this is the much more likely scenario), they will simply give up and stop reading your work, because it’s too difficult to memorize so many new terms.

Don’t give readers an excuse to stop reading. Make their life easy. Define only the acronyms that are absolutely essential to communicate your work efficiently.

Generally, this means limiting acronyms to sample names or concepts that are unique to your research.

Example: carboxylic acid-functionalized gold nanoparticles = COOH-Au-NPs

In this example, I used the common chemical abbreviation for carboxylic acid groups (COOH), the elemental symbol for gold from the periodic table (Au), and then a simple acronym for nanoparticles (NPs).

You can see how the use of too many of these kinds of acronyms could become fairly confusing for the reader, who may not immediately intuit what COOH-Au-NPs means. However, you can expect them to easily learn one or two such abbreviations in the paper. 

As a rule of thumb, I would limit the number of new acronyms you define to three or less for a journal-length publication (~3000-6000 words). That doesn’t include well-accepted acronyms, like DNA and NMR, just the terms that are wholly original to your own work. 

2) Define the acronym on first usage, then use it exclusively throughout the text after that point.

What do I mean by “define the acronym?” I mean you need to write out the full term or phrase once on first usage, then put the acronym you would like to use in parentheses following this phrase.

Example: Although Sumio Iijima is usually credited with discovering carbon nanotubes (CNTs), the history of these unique materials extends back almost 40 years prior.

After you define the acronym, you must use it throughout the text thereafter. You can’t switch back and forth between the full phrase and the abbreviation. Once the acronym is defined, you are somewhat locked into using it (with exceptions based on journal-specific guidelines for headings and captions).

Example: Carbon nanotubes (CNTs) are a one-dimensional material made of sp2-hybridized carbon. These nanomaterials can be more conductive than copper. CNTs also fluorescence in the tissue-transparent region of the near-infrared, suggesting potential applications in bio-imaging. However, the difficulty in processing CNTs has limited such proposed uses.  
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Because you’re locked into using the acronym once defined, that’s why it’s a bad idea to use too many acronyms or to define acronyms for words or phrases that are fairly common. Otherwise, your writing will become riddled with unnecessary abbreviations, which can be awkward to read or distracting.

So keep it simple. Define acronyms sparingly on first usage and then use them thereafter throughout the text. 

Hope this helps!

If you would like to learn more writing tips and tricks, check out my PowerPoint presentation An Introduction to Writing in Science, available in ebook format on the Amazon Kindle app.