There are several ways to estimate QALY. For instance, calculate the years of life remaining for a patient and weight each year with a quality-of-life score (on a 0 to 1 scale). "The basic idea underlying the QALY is simple: it assumes that a year of life lived in perfect health is worth 1 QALY (1 Year of Life × 1 Utility = 1 QALY) and that a year of life lived in a state of less than this perfect health is worth less than 1. In order to determine the exact QALY value, it is sufficient to multiply the utility value associated with a given state of health by the years lived in that state." (Prieto & Sacristán, 2003, p. 2).