If you do use an abbreviation in a running head, you can use it straightaway without definition.
Sometimes an abbreviation is presented along with an in-text citation.
For example, you might cite a test or measure that has an abbreviation and then provide its citation (for a common case, here is how to cite the ). Writing out the full term in the title will ensure potential readers know exactly what you mean, and if your article is formally published, it will ensure it is accurately indexed.
Note that if two different groups would abbreviate to the same form (e.g., both the American Psychological Association and the American Psychiatric Association abbreviate to APA), you cannot use the abbreviation in your paper—instead you must spell out the term every time to avoid ambiguity.
An exception to abbreviations in the reference list is when works have been published using abbreviations as part of the author, title, or source.
If you are unsure of the pronunciation of an abbreviation, look it up in the dictionary or ask a colleague.
If an abbreviation has multiple pronunciations, use the first one shown in the dictionary entry. Some exceptions are that you should use periods in the abbreviations for United States and United Kingdom when these terms are used as adjectives (don’t abbreviate them if they are used as nouns).
We recommend that you avoid them—for example, the reader may skim the paper before reading it in full, and abbreviations in headings may be difficult to understand out of context.
So, if a term you intend to abbreviate appears in a heading (e.g., the name of a test or measure), spell out the term in the heading and then when it first appears in the text, spell it out again and define it there.
In general, it is not necessary to use abbreviations in the abstract because the abstract is so short.
However, if the abbreviation would help the reader recognize a term or find your article via search, then it is permissible to include an abbreviation in the abstract, even if it is not used three times.