Authors

One author

• In most cases, providing the author's last name and the publication year are sufficient:
  

  Smith (1997) compared reaction times...
  
  Within a paragraph, you need not include the year in subsequent references.
  
  Smith (1997) compared reaction times. Smith also found that...

Two authors

• If there are two authors, include the last name of each and the publication year:
  

  ...as James and Ryerson (1999) demonstrated...
  ...as has been shown (James & Ryerson, 1999)...

3 - 5 authors

• If there are three to five authors, cite all authors the first time; in subsequent citations, include only the last name of the first author followed by "et al." and the year:
  

  Williams, Jones, Smith, Bradner, and Torrington (1983) found...
  Williams et al. (1983) also noticed that...

Corporate authors

• The names of groups that serve as authors (e.g. corporations, associations, government agencies, and study groups) are usually spelled out each time they appear in a text citation. If it will not cause confusion for the reader, names may be abbreviated thereafter:
  

  First citation: (National Institute of Mental Health [NIMH], 1999)
  Subsequent citations: (NIMH, 1999)