Editing Tip: Lists

A list is a simple and approachable way to present a collection of ideas. Although list formatting is relatively flexible, especially when involving bullet points, lists typically adhere to a few key rules:

Colon usage

A colon (:) is often used to introduce a list, as long as the phrase before the colon is an independent clause. The flow of the ensuing list may be enhanced by adding the term following or the phrase as follows to the independent clause.

• The inclusion criteria were as follows: age >50 years, a diagnosis of type 2 diabetes, and a history of hypertension.

Dash usage

A pair of em dashes (—) can be used to set off a list from the rest of the sentence, forming a parenthetical element.

• The inclusion criteria—age >50 years, a diagnosis of type 2 diabetes, and a history of hypertension—were strictly applied.

Comma usage

Commas (,) may be used to separate items in a list. However, the comma before the last element of a list, also known as a serial or Oxford comma, is optional, although you should remain consistent in your use or omission of this comma within a single document.

• The inclusion criteria were as follows: age >50 years, a diagnosis of type 2 diabetes, and a history of hypertension.(with serial comma)
• The inclusion criteria were as follows: age >50 years, a diagnosis of type 2 diabetes and a history of hypertension.(without serial comma)

Semicolon usage

Semicolons (;) should be used to separate complex items in a list, meaning items that already include commas. Note that the final semicolon, before the last item, is required.

• The inclusion criteria were as follows: age >50 years; a diagnosis of type 2 diabetes; and a history of hypertension, sleep apnea, and shortness of breath.

In the example above, the list includes three items, and the third includes three components, so semicolons are required.

Parallelism

Items on a list should be of the same part of speech to maintain parallel structure, thereby improving readability. For example, if a gerund is used in two items, then the verb form of the third item should be the same.

• The participants were tasked with studying the image, taking notes on its features, and discussion of their observations with the researcher.(incorrect; not parallel)
• The participants were tasked with studying the image, taking notes on its features, and discussing their observations with the researcher.(correct; parallel)

Between/among

A common misconception is that between should be used to describe a relationship between two items and that among should be used to depict the relationship of three or more items. However, according to The Chicago Manual of Style (subscription required), between “indicates one-to-one relationships,” even if more than two one-to-one relationships are implied, whereas among “indicates undefined or collective relationships.”

• No difference was observed between the control group and the experimental group.(one-to-one relationship)
• No differences were observed among the five treatment groups.(collective relationship)
• No differences were observed between the control group and the five treatment groups.(five one-to-one relationships are implied, each comparing the control group with one of the five groups)

Bulleted and numbered lists

The formatting of bulleted and numbered lists is relatively adaptable to the writer's style. In particular, punctuation may be included or omitted, and list items may be capitalized or not capitalized and composed of sentence fragments or complete sentences. Thus, the following two lists (among other possible variants) are both grammatically acceptable:

• The culture medium should contain the following:

1. DMEM
2. fetal bovine serum
3. penicillin/streptomycin

• The culture medium should contain the following:

1. DMEM,
2. fetal bovine serum, and
3. penicillin/streptomycin.

We hope that today's post has clarified conventions in list making. Please email us at [email protected] with any questions or comments. Best wishes in your research and writing!