Nov 26, 2022

Common Punctuation Errors in Research Writing

Are punctuation mistakes common?

Although our client document data shows that punctuation mistakes are somewhat less common than other types of mistakes (e.g., grammar mistakes or spelling errors) in academic texts written by non-native speakers of English, these mistakes nevertheless get in the way of conveying important information about your research to your readers. These issues also seem to be often overlooked, since authors focus on the more obvious problems when writing in a second language, such as correct vocabulary and sentence structure

However, punctuation errors are much easier to fix than many other common writing mistakes because their use is less idiomatic than that of prepositions or word choice. We will therefore not explain general punctuation rules here, but instead, list the most common types of punctuation mistakes that we find in your research papers and show you how to avoid or fix them.

Why is correct punctuation so important in research writing?

Correct punctuation is important because, without commas, periods, colons, semicolons, and dashes, your reader does not know where sentences or textual units begin and end or how they are connected. Without question marks, exclamation points, quotation marks, and brackets, they will also not understand emphasis or added tone. 

In academic writing, clarity is even more important than in other types of texts to ensure understanding of information and ideas ‒ not to mention that incorrect punctuation will make your paper or essay look sloppy and unacademic. To avoid these errors, have a look at the punctuation example sentences below, and check your texts for the common mistakes we point out before you submit or hand in your papers and assignments.

Table of Contents:

  1. Never Start a Sentence With a Numeral
  2. Don’t Use Periods in Abbreviations
  3. Don’t Let the Reader Guess ‒ Define Your Abbreviations 
  4. Spaces Before Brackets and Units (But Not Colons)
  5. Don’t Use Semicolons Like Commas
  6. Don’t Mix American and British Spelling and Punctuation 

Never start a sentence with a numeral 

NO  54% of our patients responded to the medication.

YES  Of all patients treated with heparin agents, 54% showed a good response.

YES  Fifty-four percent of our patients responded to the medication. 

Note that this is one of the exceptions to the rule that words and numerals should not be mixed. When you want to avoid starting a sentence with a numeral, it is okay to spell only the first number out and then continue with numerals according to the usual rules. 

YES   Nine percent of our patients showed immediate improvements, and a total of 17% eventually recovered.

Don’t use periods in abbreviations

Except, apparently, in the names of certain Korean idol groups (such as V.O.S, I.O.I, D.Holic, or B.A.P), periods should not be used as placeholders between initials in acronyms or abbreviations. Since a period indicates the end of a sentence or an abbreviated word, it needs to follow every initial in an abbreviation (e.g., U.S.A., a.m., Ph.D.) or only mark the end of the abbreviation, which is the case for many Latin abbreviations such as et al., etc., and ca. Note that the period often does not need to be used at all ‒ you can also simply write USA, am, and PhD. But as always, consistency is key, and you need to decide on one style and use that consistently throughout your manuscript.

NO    All participants were self-declared fans of the U.S.A team.
NO All participants were self-declared fans of either the U.S.A. team or the UAE team. 

Punctuation errors make up a large percentage of overall writing mistakes in academic papers.

Don’t make the reader guess what your abbreviations mean

An abbreviation is a shortened form of a written word or phrase that can be used in place of the whole word or phrase, just like USA, for example, is the official abbreviation of the United States of America. We use abbreviations to save space and time or to avoid repeating the same long words and phrases over and over again. Sometimes, however, we don’t even realize that a name or label we use is an abbreviation, or we are so used to abbreviating the term that we forget that the reader might not be aware of what the abbreviation stands for. 

As a general rule, all abbreviations need to be spelled out at first use, with the abbreviation following the full term in parentheses.

NO    The MWM is a test of spatial learning for rodents.

YES The Morris water maze (MWM) is a test of spatial learning for rodents.

When you have introduced an abbreviation, use only the abbreviation in the rest of your paper ‒ do not alternate between writing the full term and abbreviating it.

Note that many style guides recommend only abbreviating terms that are used at least three times in a paper and that journals also often have a list of field-related abbreviations that do not need to be spelled out at all. Some journals also ask for a list of abbreviations instead of in-text explanations or have other specific guidelines. Always check the recommendations of the relevant style guide (e.g., APA style) and the target journal before finalizing your manuscript.

Add spaces before brackets and units (but not colons)

Brackets and parentheses need to be separated from text by a single space (before and after) ‒ imagine that you need to let them “breathe” a little. 

NO    The control group(recruited at the same school)was larger than the test group. 

YES   The control group (recruited at the same school) was larger than the test group. 

Note that punctuation marks (commas, colons, periods) immediately follow brackets or parentheses.

NO    Results were analyzed according to age (except for the variable “education”) . 

YES   Results were analyzed according to age (except for the variable “education”).  

You also need to add a single space between a number and any unit of measurement.

NO    The control mice measured 5cm, 6.5cm, and 8.2cm, respectively. 

YES   The control mice measured 5 cm, 6.5 cm, and 8.2 cm, respectively.

When a measurement is used as an adjective describing a noun, however, the space is replaced by a hyphen.

NO    A 5 sec interval was inserted between detection trials.  

YES   A 5-sec interval was inserted between detection trials.  

Spaces before and after mathematical symbols are also important when it comes to consistency and readability. You can generally include or omit a space both before and after a symbol (but check the target journal guidelines for specific rules), but be consistent when using each symbol as well as applying them within your paper. If you report p-values as p<0.05 in your abstract, you should not suddenly change that to p = 0.013 in your result section.

Where you do not add an extra space is before colons ‒ like commas, semicolons, and periods, colons follow the letter (or brackets/parentheses) directly.

NO    Different intervals were inserted between detection trials : 4 sec, 5 sec, and 2 sec.  

YES   Different intervals were inserted between detection trials: 4 sec, 5 sec, and 2 sec.

Don’t use semicolons like commas

The semicolon is often described as “stronger than a comma” but “weaker than a period” ‒ but it is not usually a replacement for either of those punctuation marks.

Two independent clauses can be separated by a period, but they can also be separated by a semicolon if (and only if) they are closely connected.

NO    My brother lives in Spain; on Christmas, the whole family will meet again.

YES  My brother just entered Korea University; he is majoring in clinical psychology.

YES  Birth rates have been falling for years; consequently, less and less students enter university every semester.

Semicolons are also used, instead of commas, to separate listed items that are not just single words but already contain punctuation (such as commas and dashes). Using commas inside and between such list items can sometimes make it very difficult for the reader to follow.

NO   Participants were recruited at several different locations, including the Charite Hospital ‒ the only participating institution with a specialized department in this area ‒ in Berlin, Germany, Samsung Medical Center in Seoul, Korea, and Tokai University Hospital in Tokyo, Japan.

YES  Participants were recruited at several different locations, including the Charite Hospital ‒ the only participating institution with a specialized department in this area ‒ in Berlin, Germany; Samsung Medical Center in Seoul, Korea; and Tokai University Hospital in Tokyo, Japan.

Don’t mix American and British spelling and punctuation 

While it is obvious that an article or paper should be consistently written in either American or British English, authors often forget that there are not only differences in spelling and word choice but also in punctuation and that all of these elements need to be consistent. 

For example, it is important to differentiate between American double quotation marks and British single inverted commas, and your choice should be in line with your spelling.

NO    Behaviour was measured with items rated on a 5-point scale, ranging from 1 = “strongly disagree” to 5 = “strongly agree”.

YES   Behaviour was measured with items rated on a 5-point scale, ranging from 1 = ‘strongly disagree’ to 5 = ‘strongly agree’.

YES   Behavior was measured with items rated on a 5-point scale, ranging from 1 = “strongly disagree” to 5 = “strongly agree”.

Another important difference between American and British English conventions is the “Oxford comma”. Although named after a British university, this comma, which is placed before the and that precedes the final item in a list, is considered standard in many US style guides but not common practice in the UK. In general, it is up to you if you want to use it or not, and most journals will not consider it inconsistent to use the Oxford comma in a manuscript that is written in British English, because it can sometimes avoid ambiguity. But keep in mind that, as always, you need to stick to the same style throughout your manuscript.

For a free grammar checker that corrects your academic writing, check out Wordvice AI today. Then visit for professional editing services, including paper editing and manuscript editing, by human editors before submitting your manuscript to journals.

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