It was found that individual preferences over health are influenced by the duration of health states and their sequence .
However , although there is much variation across individual respondents , the assumptions tend to hold much better when valuations are aggregated across respondents , which is encouraging for economic evaluations that rely on using average ( mean or median ) values
The numbers of quality -adjusted life years ( QALYs ) gained are increasingly being used to represent the gains in individual utility from treatment .
This requires that the value of a health improvement to an individual is a simple product of gains in quality of life and length of life .
The article reports on a systematic review of the literature on 2 issues : whether the value of a state is affected by how long the state lasts , and by states that come before or after it .
Tests of Preferential Independence in the QALY Model
The author presents evidence for the descriptive adequacy of the  quality -adjusted life years ( QALY ) model as applied to health profiles . One important assumption of the model is preferential independence : if two profiles have the same health state during year X , then preference between them does not switch if the level of health changes during year X. In experiment 1 , 30-year health profiles were used to perform 27 em pirical tests of independence with 98 subjects .  Independence was reliably satisfied in all 27 tests . In experiment 2 , 15 additional tests were conducted . These tests had been specifically design ed to be more sensitive to independence violations , but indepen dence was still mostly satisfied . In both experiments , the conclusions about indepen dence hold regardless of what discount rate is used . These results act as a " lower bound " on the validity of the QALY model for health profiles . Key words : quality -ad justed life years ; QALY model ; health profiles ; preferential independence . ( Med Decis Making 1998;18:418 - 428
It was found that individual preferences over health are influenced by the duration of health states and their sequence .
However , although there is much variation across individual respondents , the assumptions tend to hold much better when valuations are aggregated across respondents , which is encouraging for economic evaluations that rely on using average ( mean or median ) values
The numbers of quality -adjusted life years ( QALYs ) gained are increasingly being used to represent the gains in individual utility from treatment .
This requires that the value of a health improvement to an individual is a simple product of gains in quality of life and length of life .
The article reports on a systematic review of the literature on 2 issues : whether the value of a state is affected by how long the state lasts , and by states that come before or after it .