Nowadays, most complaints about the ambiguity of the concept of quality of life (QoL) are unjustified: QoL can be defined, definitions can be adapted to different settings and patients, and QoL can be separated from other concepts. The problem is: you need to be on top of the literature in order to choose a definition, and to understand the consequences of your choices. For palliative care, in my view, there is a conceptualisation that is most applicable: individual QoL.
Admittedly, describing the characteristics of the concept of QoL can be confusing. First, there is consensus about aspects of QoL that apply to all populations:
Different concepts apply to different populations:
There are subtle differences regarding the content of QoL:
Thus, when addressing the concept of QoL, you need to be aware that you may be confronted with a specific combination of the above (e.g., perceived functioning of a patient regarding a number of cancer-specific aspects of life, such as pain, nausea, fatigue, body image).
A problematic aspect about the concept of QoL is the choice of dimensions. This choice is influenced by the choice of focus: general, health-related, or disease-specific. It is very appealing to determine a set of dimensions that is relevant to all individuals within a population. After all, with a universal set of dimensions, all individuals can be easily compared, and it is very clear in which area's interventions may be applied. In most HRQoL and disease-specific QoL conceptualisations, dimensions have been determined by e.g. using patient groups, experts, statistical tests. Indeed, in order to compare groups, or to study the effect of e.g. a treatment on a specific aspect, these conceptualisations are useful.
Fact is that except perhaps on a very general (and thus less useful) level, individuals will differ in what they feel is important. The 'weight' of dimensions will differ from individual to individual. What is important to an individual is almost impossible to predict (again, except on a general level), because too many influences may determine these areas: age, gender, economic conditions, living conditions (e.g. being homeless), psychological dispositions (e.g. optimism), disease (e.g. life-threatening disease, life events (e.g. loss of a spouse), physical discomfort (e.g. pain), societal circumstances (e.g. war), culture, and many more. In addition, these factors may change over time, and the way they interact may change over time. Note that these factors do not necessarily determine how well individuals are doing regarding their QoL; they determine, to some extent, the content of QoL, i.e., the dimensions.
It is conceivable that the turmoil described above is especially salient at the end of life: the diagnosis of serious illness, the physician's message that the illness has advanced beyond cure, the pain, and many more aspects may contribute to this turmoil.
It is thus probable that fixed / standardised QoL dimensions will not reflect the aspects that individuals feel are important in their lives at a certain point in time. The conclusion can only be that individuals should be asked about the content of their QoL, especially at the end of life. An individual approach is necessary for a comprehensive assessment of QoL at the end of life.
In individual QoL (IQoL) content preferences and levels of QoL are determined by the individual. Typically, when assessing IQoL, individuals are asked which dimensions are important for their QoL. In a next step, individuals are asked to evaluate the dimensions, or rate their functioning within each dimension. In a last step, individuals are asked to determine the relative importance or weight of each dimension, because not all dimensions may be seen as equally important, and the evaluations of the different dimensions should thus not contribute equally to global QoL--the outcome of IQoL.
Although the content (dimensions) of IQoL will differ among individuals, IQoL outcomes are comparable between individuals. Within individuals, IQoL may well change over time as well. If you're interested in following or comparing patients regarding specific dimensions of QoL (and thus disregarding that in reality the importance of these dimensions may vary between and within individuals), IQoL is not suitable.
We did two studies on individual QoL in patients at the end of life. See this publication and this one (PubMed abstracts). In these studies, we used the Schedule for the Evaluation of Individual QoL - Direct Weighting version SEIQoL-DW. Click here for some basic information on the SEIQoL-DW.