Quality of Life
QoL has recently emerged as an important indicator of clinical significance. Health care providers and funding agencies are increasingly requiring that indexes of QoL be incorporated in assessments of treatment effectiveness. One difficulty with including measures of QoL in studies of behavioral intervention is identification of the appropriate metric. There is no agreed-upon strategy for measuring QoL as it represents a multidimensional construct that includes a broad range of life domains and it is shaped by both objective and subjective factors. Generally, QoL includes physical well-being, social well-being, and emotional well-being as well as behavioral competence or the ability to effectively engage in valued life activities. Definitions of QoL have included a number of concepts including life satisfaction, social support, psychological well-being, social and emotional functioning, and standard of living. Lawton (1983) eloquently defined QoL as a multidimensional evaluation, by both personal- and social-normative criteria, of the person-environment system of an individual in time past, current, and anticipated. In essence, QoL is a type of umbrella construct that includes health states and satisfaction with a number of life domains.
An aspect of QoL that is particularly relevant to behavioral intervention studies is health-related QoL (HRQoL), where QoL is considered in the context of health and disease. HRQoL is also a multidimensional construct that includes domains related to physical, emotional, and social functioning and focuses on the impact of health status on QoL or the QoL consequences of health status.
There is a wide variety of QoL measures that have been used in studies assessing treatment effects. These measures generally fall into two categories: measures of generic QoL and measures of HRQoL. Generic measures can be applied to both healthy and ill individuals and tend to cut across a broad range of domains. Measures of well-being, social support, and life satisfaction are typically placed in this category (e.g., the Satisfaction With Life Scale; Diener et al., 1985). The World Health Organization (WHO) has developed what is intended to be an international, cross-culture measure of QoL—WHOQOL-BREF, a 26-item instrument, which measures physical health, psychological health, social relationships, and the environment (WHO, 1996).
There are numerous HRQoL measures (e.g., Short-Form Health Survey [SF-36], Sickness Impact Profile [Bergner et al., 1981]; Quality of Well-Being Scale [Kaplan & Bush, 1982; Ware & Sherbourne, 1992]) available. Haywood, Garratt, and Fitzpatrick (2005) provide a review of the measurement properties of many of these instruments for older people. Generally, HRQoL measures are intended to assess the impact of illness on QoL. Although these measures may include some items related to overall QoL or life satisfaction, their primary emphasis is on symptoms, impairment, function, and disability. The Patient Reported Outcomes Measurement Information System (PROMIS; www.nihpromis.org) includes a 10-item global health measure, which assesses global physical, mental, and social HRQoL. PROMIS is part of the National Institutes of Health (NIH) Roadmap initiative that was designed to develop an electronic system to collect HRQoL from diverse populations.
More recently, an emphasis has been placed on Quality-Adjusted Life Years (QALYs), which is a single index that combines quality of remaining life years with survival data. QALYs have two basic components: the quantity and quality of life. It is used to measure the extent of health gains from a health care intervention related to the cost associated with the intervention to assess the worth of an intervention from an economic prospective. Of course, there are shortcomings associated with using QALYs as outcome measure. For example, QALY represents a single index and excludes other health-related consequences, has limitations with respect to sensitivity, and does not give sufficient weight to emotional and mental health issues. In addition, QALY does not appear to work well with complex interventions (Normand, 2009; Phillips, 2009).
When selecting a measure of QoL, it is important to establish an operational definition of QoL relevant to the intervention being evaluated and the target population (e.g., burden associated with caregiving). In some cases, it might be advisable to include more than one measure of QoL in an assessment battery. It is also important to recognize that, for many of the QoL instruments, it is difficult to interpret scores and magnitude of change in terms of clinical relevance. Of course, the general criteria for selection of outcome measures outlined in Chapter 14 need to be considered.