* First introduced in 1974 by Cullen DJ, Civetta JM, Briggs BA, et al: Therapeutic scoring systems: A method of quantitative comparison of patient care. Crit Care Med 2:57-60, 1974) at the Massachusetts General Hospital. (TISS with 70 therapeutic variables).
* Modified in 1983. (TISS with 76 therapeutic variables).
* Modified version in 1994 for use for intermediate and floor care nursing units (iTISS).
* Modified version in 1996. (TISS with 28 therapeutic variables).
* ICU in the City of Winnipeg uses a locally modified version of the 1983 TISS-76 and has a list of 83 therapeutic variables.
* TISS is a method of quantifying nursing and medical care required by ICU patients
* TISS has become a widely accepted and validated method of classifying critically ill patients.