If a compound adjective can be misread, use a hyphen.
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
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
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-centred counselling but the counselling was client centred
t-test results but results from t tests
same-sex children but children of the same sex
Write most words formed with prefixes and suffixes as one word.
Prefixes
aftereffect
extracurricular
multiphase
socioeconomic
Suffixes
agoraphobia
wavelike
cardiogram
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