1. American Heritage Dictionary of the English Language (4th ed.). Retrieved September 05, 2006, from Dictionary.com: http://dictionary.reference.com/search?q=competence.
2. (Ed.) (1998). The competency casebook. Amherst, MA: HRD, & Silver Spring MD: International Society for Performance Improvement.
3. Beyond mere competency: Measuring proficiency with outcome proficiency indicator scales
4. (1996). Human Competence. Silver Spring, MD: International Society for Performance Improvement.