How do I know that I have to put a hyphen in a compound word.

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.

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

• capitalised: 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