When do you need to use a hyphen for compound words (APA)?

When do you need to use a hyphen for compound words (APA)?
General Principle 1
Do not use a hyphen unless it serves a purpose. If a compound adjective cannot be misread or, as with many psychological terms, its meaning is established, a hyphen is not necessary.
For example
• covert learning techniques
• health care reform
• day treatment program
• sex role differences
• grade point average
General Principle 2
In a temporary compound that is used as an adjective before a noun, use a hyphen if the term can be misread or if the term expresses a single thought (i.e., all words together modify the noun).
For example:
• "the adolescents resided in two parent homes" means that two homes served as residences, whereas if the adolescents resided in "two-parent homes," they each would live in a household headed by two parents.
A properly placed hyphen helps the reader understand the intended meaning.
Also use hyphens for
Compounds in which the base word is
• capitalized: pro-Freudian
• a number: post-1970
• an abbreviation: pre-UCS trial
• more than one word: non-achievement-oriented students
All "self-" compounds whether they are adjectives or nouns
• self-report
• self-esteem
• the test was self-paced
Exception: self psychology
Words that could be misunderstood
• re-pair [pair again]
• re-form [form again]
• un-ionized
Words in which the prefix ends and the base word begins with the same vowel
• meta-analysis
• anti-intellectual
• co-occur
General Principle 3
Most compound adjective rules are applicable only when the compound adjective precedes the term it modifies. If a compound adjective follows the term, do not use a hyphen, because relationships are sufficiently clear without one.
• client-centered counseling
but
the counseling was client centered
• t-test results
but
results from t tests
• same-sex children
but
children of the same sex
General Principle 4
Write most words formed with prefixes and suffixes as one word.
Prefixes
• aftereffect
• extracurricular
• multiphase
• socioeconomic
Suffixes
• agoraphobia
• wavelike
• cardiogram
General Principle 5
When two or more compound modifiers have a common base, this base is sometimes omitted in all except the last modifier, but the hyphens are retained.
• Long- and short-term memory
• 2-, 3-, and 10-min trials
See the Publication Manual for exceptions to these principles.
This article originally appeared on http://www.apastyle.org/learn/faqs/when-use-hyphen.aspx

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