Parallel ideas, that is, ideas being compared (APA 3.09), coordinated (APA 3.23), listed (APA 3.04), or presented as stubs in a table (APA 5.13), must be expressed using parallel grammatical forms. In other words, the ideas need to have a similar grammatical structure (e.g., adjectives with adjectives, verbs with verbs, nouns with nouns, and so on).

Key: yellow, bold = conjunction (connector) green, underline = words/phrases that should be parallel or that are incorrectly presented as parallel

Comparisons

CORRECT:
These average levels were higher than they had been in previous studies.

INCORRECT:
These average levels were higher than previous studies.

CORRECT:
Another finding was that women reported more of these incidents than men did.

INCORRECT:
Another finding was that women reported more of these incidents than men.

Note: In both of the incorrect versions above, the comparisons are not logical because of the sentence structures used. Faulty parallel structures can lead to unintended comparisons.

Between. . . and

CORRECT:
Researchers have speculated about the differences between the caregiver burden experienced by adult children and the caregiver burden experienced by spouses.

INCORRECT:
Researchers have speculated about the differences between the caregiver burden experienced by adult children and spouses.

Note: In the incorrect version, the author appears to be comparing a burden to a group of people.

CORRECT:
Participants in that study included adolescents between 13 and 18 years of age.

INCORRECT:
Participants in that study included adolescents between 13–18 years of age.

INCORRECT:
Participants in that study included adolescents between 13 years of age and 18.

Note: One of the incorrect versions has a hyphen instead of the coordinator and. In the other, only the number 13 is modifying the phrase years of age because of word order.

 

Both. . . and

CORRECT:
The researchers collected data through both qualitative interviews and quantitative surveys.

INCORRECT:
The researchers collected data both through qualitative interviews and quantitative surveys.

Note: In the incorrect version, the phrases the writer is correlating have different grammatical structures: one is a prepositional phrase, and the other is a noun phrase. For the preposition through to apply to both items, it needs to precede the word both.

 

Neither. . . nor and either. . . or

CORRECT:
The medium effect size allowed for analysis that was neither too strict nor too lenient in assessing relationships between the variables.

INCORRECT:
The medium effect size allowed for analysis that was neither too strict nor lenient in assessing relationships between the variables.

Note: In the incorrect version, the word too is modifying only strict, not lenient. For too to apply to both adjectives, it needs to appear after both neither and nor.

 

Not only. . . but also

CORRECT:
Member checking ensures that the data collected are not only transferable but also accurate.

INCORRECT:
Member checking ensures not only that the data collected are transferable but also accurate.

Note: In the incorrect version, the words not only are followed by a that clause, whereas the words but also are followed by an adjective. The structure that follows not only should be grammatically equivalent to the structure that follows but also.

 

Lists (items in a series)

CORRECT:
In this chapter, I explain the research design, the rationale, and the variables.

INCORRECT:
In this chapter, I explain the research design, the rationale, and describe the variables.

Note: In the incorrect version, two of the coordinated items are noun phrases and one is a verb phrase.

CORRECT:
Four major themes emerged from the data: (a) well-planned on-boarding, (b) peer mentoring, (c) asking about employees' needs, (d) and engaging employees.

INCORRECT:
Four major themes emerged from the data: (a) well-planned on-boarding, (b) the use of peer mentors, (c) ask what employees need, (d) and engage employees.

Note: In the incorrect version, two of the listed items are noun phrases and two are verb phrases. In the correct version, all items have a similar structure (i.e., a phrase containing a gerund, or -ing form of the verb).

 

For more help with parallel structure in a series or list, see this blog post from the APA style blog.