Abstract
This chapter provides an introduction to a variety of essential issues concerning quality of life (QoL) as a social-scientific construct. The chapter begins with an introduction to the notion of QoL as an essentially contested concept and provides a taxonomy for classifying various instruments. The various methods of operationalizing the measurement of health-related quality of life (HRQoL) are outlined and a variety of practical examples are provided. A range of methods of determining the validity, reliability, and responsiveness of QoL measures are discussed to provide the reader with the tools necessary to critically evaluate the broad range of QoL instruments available. Finally, the scope of employment of QoL instruments is explored and several important limitations of this mode of assessment are discussed.
TopConceptualization Of Qol
An accurate definition of a concept should strive to be both exhaustive and exclusive. That is to say, a definition should include all that is pertinent, while excluding all that is not. Clearly, meeting these criteria is often not possible, yet, it has been noted that moving toward this ideal is more difficult with some concepts than with others. Such is the case with quality of life (QoL). Put simply, there is no one definition of QoL (Hunt, 1997). Although many definitions have been proposed, each has its own limitations (Power & Kuyken, 1998). In many ways, QoL can be recognized as an “essentially contested concept” (Gallie, 1964). An essentially contested concept is one that has widespread agreement about its existence and its core “notion”, but significant debate exists about both its full meaning and operationalization. Put more practically, it is not a matter of further philosophical debate or empirical research which will furnish a more “correct” definition of QoL; but rather, even in principle, it is not possible to arrive at its conclusive definition. QoL is a socially constructed concept and it can hold different and equally valid meanings for different people. This “relativity” stems from the fact that there is no objective referent object that individuals can turn to in order to decide what should and should not be included in its definition. It is a latent construct. Given the inherent instability of QoL as a concept, many have questioned its utility as a practical tool in research and decision-making. Yet, there are many essentially contested concepts that have proven to be very important to society. Few would argue that the concepts of democracy, peace and justice remain important despite their essentially contested nature. In a similar fashion, QoL is a concept that has proven to be useful in understanding both individual and collective self-perceptions. In light of these considerations, defining QoL can be described as an exercise in both stipulation and negotiation. Finding common, relevant ground for the content within QoL surveys is accomplished in a variety of ways; most often through focus groups and expert agreement. The process of stipulation can be either explicit, wherein an author states the breadth of phenomena intended to be measured; or implicit, wherein one is left to surmise the phenomena intended to be measured by the content of the questions employed. In common practice the latter is far more often encountered than the former (Gill & Feinstein, 1994). In either case, it is important to determine what a QoL instrument is intending to measure. With this in mind, the following sections will now address the practical art of measuring QoL.
Key Terms in this Chapter
Item Response Theory: A school of psychometric thought that holds that individual responses to questions on a survey are a probabilistic function of both respondent traits, as well as traits inherent to the questions themselves.
Time Trade Off: A form of assessment based on utility theory used in quality of life research that is intended to illicit a respondent’s preference for complete health based on the number of years of their remaining life they would be willing to give up to attain perfect health.
Visual Analogue Scale: A form of assessment that asks respondents to provide their rating of a question on a numeric linear scale that traditionally ranges from zero to one hundred.
Conjoint analysis: A method of utility assessment that asks respondents to rank order their preferences for a series of alternatives, which can be presented in a variety of formats including rating, ranking or more often, discrete choices between a series of pairwise comparisons.
Standard Gamble: A method of assessment based on utility theory used in quality of life research that is intended to obtain a respondents preference for perfect health by determining the amount of risk of sudden death an individual would be willing to accept in order to attempt a treatment that would restore them to perfect health - if it worked.
Likert Scaling: A method of selecting items for inclusion in surveys that are intended to study a singular underlying construct using an ordinal response set.
Factor Analysis: A statistical method used to classify large numbers of interrelated measurements into a smaller selection of factors that represent larger underlying constructs.
Guttman Scaling: A method of creating measurement scales that assess a single underlying construct using questions that can be ordered along a continuum that represents increasing attitudes held by respondents toward the underlying construct being investigated.
Internal Consistency: Statistical tests which determine to what degree test items are related to each other. The most frequently employed statistic is Cronbach’s alpha coefficient.