by David Becker
A common mistake people make is to include apostrophes when pluralizing a number or an abbreviation. Apostrophes are generally used in contractions and to indicate the possessive case, but they are not used to form plurals of numbers and abbreviations in APA Style.
For instance, writing “the 1960’s” when referring to that entire decade is incorrect; instead, one should write “the 1960s.” The same rule applies to the plural form of any other type of number, such as describing someone’s age (e.g. “clients in their 80s”), and is discussed further in section 4.38 on page 114 of the Publication Manual.
A similar rule in section 4.29 on page 110 applies to abbreviations. Just as with numbers, don’t include an apostrophe when pluralizing abbreviations. For example, when pluralizing an acronym, such as “CV” for “curriculum vitae,” all you need to do is add an s to the end, as in “CVs.” This rule also applies to standalone letters, as in “The students all received As.” For abbreviations that end with a period, such as “Ed.” to indicate an editor in a reference list entry, add an s before the period, as in “Eds.” When pluralizing an italicized abbreviation, remember not to italicize the s, as in “ps.” Just don’t add an apostrophe.
For more information, take a look at our other posts on punctuation in APA Style. Punctuation is also covered in more detail on pages 87–96 of the Publication Manual. And, of course, please feel free to comment on this post or contact us with any of your style questions.