title: Proportional Heuristics in Time Tradeoff and Conjoint Measurement Comparing Three Versions of the Time Tradeoff A cost utility analysis of treatment options for gallstone disease: methodological issues and results. Tests of Preferential Independence in the QALY Model The utility of different health states as perceived by the general public.
abstract: The time-tradeoff ( TTO ) test is widely used to measure quality of life for different health states . Subjects are asked to equate the value of living a given period in an inferior health state to the value of living a shorter period in good health . Applications of TTOs have been criticized based on the fact that the value of future life duration is taken as the future life duration itself . The authors show that for a health state in which a subject does not want to live longer than a specified amount of time , subjects ' responses do not comply with the assumption that the value of the period in inferior health is equated to the value of the shorter period in good health Actually , preference reversals with respect to such a health state point to the use of a proportional heuristic in the TTO test . Comparisons of the TTO test in these subjects with category scaling and difference measurements also favor a proportional inter pretation of the TTO test . In tests based on conjoint measurement , these subjects also appear to use a proportional heuristic . Consequences of the use of the TTO test and conjoint measurement m quality -of-life models are discussed Key words : utility assessment , QALY , conjoint measurement ; preference reversals ; compatibility effect . ( Med Decis Making 1996;16:36 - 44 This paper reports a comparative study of three formulations of the time-tradeoff ( TTO ) method of health valuation . One asks people to consider giving up time each day in exchange for better health . The second asks people to consider giving up time during a 12-month interval . The third is the more conventional TTO in which people are asked to contemplate a reduction in life expectancy . Question naires were sent to 4,087 adults selected at r and om from the population of Scotl and . Each respondent provided a de scription of his or her health , and was asked to value an improvement in that health , using all three formulations of the TTO . The daily TTO appeared to be an improvement on the conventional formulation , correlating more strongly with health , eliciting re sponses that appeared to be more precise , and obtaining information about the value of health from a far greater number of respondents . The performance of the annual TTO appeared to be only slightly inferior to that of the daily TTO . Key words : time tradeoff ; quality of life ; health valuation . ( Med Decis Making 1996;16:335 - 347 The techniques of cost utility analysis ( CUA ) were used to evaluate the treatment of gallstone disease by open and laparoscopic cholecystectomy and by extracorporeal shockwave lithotripsy ( ESWL ) .  The application of the techniques in this context raised three method ological questions which are not satisfactorily resolved in the literature . The first is whether an ex ante or ex post perspective is best adopted for the measurement of quality of life ( QoL ) . The second is the method for converting a short term deterioration in QoL followed by full health into QALYs and the reliability of the methods available . The third is the issue of indirect costs which , in the context of a temporary disease state , can not be easily avoided . The economic evaluation found laparoscopic cholecystectomy to be generally superior than the competitor technologies ( entailing lower costs and better outcomes ) . However , the results were sensitive to assumptions about the perspective for measuring benefits and the inclusion of indirect costs 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 A series of ‘ scenarios ’ describing the physical , social and emotional characteristics , limitations and duration of different health states have been successfully applied to a r and om sample of the general public in order to determine their social utility . The result ing mean daily health state utilities differ among disorders and vary with age , the duration of the disorder , the ‘ label ’ used to describe the disorder and the health status of the respondent . These health state utilities have considerable potential application in the planning and financing of health services
target: 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
background: 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 .