References:
George, J. (1990). Nursing Theories: The Base for Professional Nursing Practice; 4th Edition. London: Prentice-Hall International, Inc. p. 317.
McEwen, M. & Wills, E. (2007). Theoretical Basis for Nursing; 2nd Edition. Philadelphia, USA: Lippincott Williams & Wilkins. p. 191.
Tomey, A.M. & Alligood, M. (2002). Nursing Theorists and their Work; 5th Edition. Singapore: Mosby, Inc. p. 145.
Tomey, A.M. & Alligood, M. (2006). Nursing Theory Utilization and Application; 3rd Edition. Missouri, USA: Mosby, Inc. p. 103
Watson, J. (1985). Nursing: Human Science and Human Care. Connecticut, USA: Appleton-Century-Crofts.
http://www2.uchsc.edu/son/caring/content/evolution.asp
