[Assessment of health related quality of life--Part 1--Direct measures]

Assessment of the impact of medical interventions on patient's quality of life is becoming a major aspect in evaluating the effectiveness of these interventions. Based on the concept of combining life expectancy and quality of life in a single value, many tools for measuring this effect have been developed in the last few decades. Quality-adjusted life years (QALYs) are calculated by multiplying life expectancy by a factor representing the quality of life during that period. Health related quality of life may be measured directly by several methods. The most commonly used are Visual Analogue Scale (VAS), Standard gamble (SG) and Time Trade-Off (TTO). This article reviews these three methods, their applications and their advantages and disadvantages. It also addresses some of the problems characteristic of each measure, their theoretical and practical differences and the implications of those differences on the values obtained from each one. Finally, the article discusses the attempts to map the relationships between the three measures, in order to be able to convert values from one to another.