To cite software, use the following form:
1. Epi Info [computer program]. Version 3.2. Atlanta, GA: Centers for Disease Control and Prevention; 2004.
2. Intercooled STATA (for Windows) [computer program]. Version 7.0. College Station, TX: StataCorp; 2000.
Software need not be cited in the reference list if it is mentioned only in passing or is available without charge via the Internet (eg, shareware or freeware).