APA format is introduced by American psychological Association(APA). Here are their abreviation guidelines - Use s for second, m for meter. -e.g. [use for example] - etc. [use and so forth] - i.e. [use that is] - viz. [use namely] - vs. [use versus] - Do use "pp." for citations of encyclopedia entries -To form plurals of abbreviations, add s alone, without apostrophe (PhDs, IQs, vols., Eds). - Use two-letter postal codes for U.S. State names. For more information , visit >>> www.psychwww.com