Apostrophes: possession, contraction and plurals
An apostrophe can mark possession or omitted letters. Its position distinguishes singular and plural possessors, while ordinary plural abbreviations and possessive pronouns do not need one. Recasting a sentence can remove an awkward possessive without losing its meaning.
Possessive nouns and pronouns
A singular noun normally forms its possessive with apostrophe-s, as in the patient's medical record or George's new car. A plural already ending in s takes the apostrophe after that letter, as in patients' medical records, the Smiths' new car, the rashes' development and the classes' projects. Possessive pronouns such as its, theirs, his and hers take no apostrophe. An acute or grave accent is not an apostrophe and should not be typed in its place.
A singular name ending in s can take either an apostrophe alone or apostrophe-s: Dr. Jones' and Dr. Jones's, or Bill Thomas' and Bill Thomas's. The chosen form should be used consistently. For a couple called Thomas, the plural name is the Thomases and its possessive is the Thomases'. If the expression looks or sounds muddled, it can be recast as the new car Bill Thomas bought.
A supply lasting one day is a day's supply or one day's supply; one lasting seven days is 7 days' supply. A hyphenated adjective, such as a 6-day supply or a 7-day supply, avoids the possessive.
Contractions and its
An apostrophe can show that one or more letters have been omitted. A strict approach to formal scientific style rejects contractions such as won't, wouldn't, they're, can't, would've and it's, recommending that the words be written out in full.
In “It's my car”, it's means it is; in “Its tires were bald”, its expresses possession. The possessive form is always its, with no apostrophe before or after the s.
Plural abbreviations and letters
Plural abbreviations that do not express possession need no apostrophe: IECs, IRBs and CRFs denote institutional ethics committees, institutional review boards and case report forms. Apostrophes can distinguish the plural letters in the expression mind your p's and q's.
Possessives before -ing forms
In “We approve his coming”, the possessive directs the approval towards the coming; in “Bill's playing is hopeless”, the assessment concerns the playing. The corresponding possessive forms include “The director spoke about John's having finished the job”, or his having finished the job, and the students' having completed a field experience.
A formal-usage recommendation favours “He resents my going” and offers a noun-substitution test: replacing going with departure gives the correct “He resents my departure”, whereas “He resents me departure” is incorrect. Under that test, an -ing form used as a noun takes a preceding possessive. Where the construction remains doubtful, recasting the sentence can make it correct and readable.
Recasting and descriptive names
A compound noun or prepositional phrase can avoid a possessive: drug profile replaces drug's profile, and the medical record of the patient replaces the patient's medical record. Restructuring can also remove a possessive that makes readers stop to check its meaning.
In a survival-study example, “To investigate survival, the patient's status was followed-up monthly” leaves a question about whether one patient or each patient is intended. Changing it to “the patients' status” establishes that more than one patient is meant, but may still prompt readers to check the apostrophe. “To investigate survival, the status of the patients was followed up monthly” removes the apostrophe at the cost of lengthening the sentence. Because follow-up to investigate survival already concerns patient status, the sentence can become “Patients were followed up monthly to investigate survival”, eliminating status, the apostrophe and the introductory comma.
European Medical Writers Association has no apostrophe: the name can be understood as an association of or for medical writers rather than a possessive. An ownership interpretation can support an argument for an apostrophe; where competing interpretations have equal weight and no authority settles them, choosing the reasoning that gives the most straightforward text is one recommended approach.