The term quality of life is used frequently in everyday life, with most people assuming they know what it means without considering how to define or measure it. In terms of health, QoL has become a popular, broadly used expression that is frequently taken for granted without the meaning being clear. There is debate about the true def inition and meaning of QoL, particularly whether ratings should be objective or subjective, what criteria should be used and what is actually being measured, ‘the quality of an individual’s life, state of life, or the meaning of life in general’⁸. QoL is argued to be less related to basic needs than to individual expectations and expe riences of life, which include individual perceptions of well-being, happiness, goodness and satisfaction with various aspects of their lives and environment^9-11. What is apparent is that QoL is a multi dimensional concept ‘just as is life itself’¹². A wide range of domains is suggested for inclusion as QoL indicators, including physical and mental health, intellectual and emotional function, social and role function, activities of daily living, economic aspects, and job and life satisfaction^13-15. The expression QoL may also overlap with the terms ‘health status’ and ‘functional status’, and have been consid ered interchangeable¹⁶. Perceptions of well-being may, however, be influenced by psychological factors unrelated to health or function¹⁷.

There are several meanings of the term QoL, which remains a vague, elusive concept for which there is no single widely accepted defini tion. The definitions provided are broad and varied; indeed, there may be as many QoL definitions as there are people¹⁸. QoL is viewed as ‘a concept which incorporates all aspects of an individual’s existence’¹⁹ and as ‘an abstraction which integrates and summarizes all those fea tures of our lives that we find more or less desirable and satisfying’²⁰. The inclusion of the terms life satisfaction, morale and happiness are debated but may be considered to be transient states which should be distinguished from QoL as they differ in their degree of subjectivity²¹. Alternatively, life satisfaction, self-esteem and phys ical health are argued to be key dimensions of QoL²². Lawton²³ defines QoL as ‘the multidimensional evaluation, by both intrap ersonal and social-normative criteria, of the person-environment system of an individual in time past, current and anticipated’ and hypothesizes four dimensions of QoL: behavioural competence, per ceived QoL, objective environment, and psychological well-being. Each sector is intrinsic and considered core to the concept of QoL and also interlinked. Fundamentally, QoL is perceived as being con tinuous and dynamic in nature and may be evaluated negatively or positively depending on the individual’s own internal perceptions and response to their environment.

Within the context of health, QoL is defined as a reflection of patients’ perception and response to their health status and to other non-medical aspects that have an impact on patients’ lives, and within health-related quality of life (HRQoL) this includes physical, psychological and social perspectives^24,25. This definition is in keeping with that given by the World Health Organization Quality of Life Group (WHOQOL), as ‘the individuals’ perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards and concerns’²⁶. This broad description encompasses the complex nature of the person’s physical, psychological and social well-being in relation to their environment. The recognition of cultural factors is particularly important when considering the QoL of the ageing population and especially those people with dementia. Memory impairment is not regarded as so important in all cultures²⁷. Similarly, functional disability may seem less important in cultural contexts where independence and autonomy in activities of daily living are a less central part of the older person’s role²⁸. Older people are frequently marginalized as society holds a negative view of their QoL, and health and social research tends to focus on decline and disability²⁹. There are, however, both positive and negative elements that impact on an older person’s QoL, and Hughes³⁰ identifies the key domains that should be evaluated when measuring older people’s QoL. These include physical environment, social environment, socioeconomic, cultural and health status, personality and personal autonomy factors.

Lerner³¹ argues that ‘health is more than just a biomedical phe nomenon; it involves a social human-being functioning in a social environment with social roles they need to fulfil’. The use of QoL as an outcome measure focuses the impact of the patient’s condition and treatment on their emotional and physical functioning and lifestyle³. Hence, health-related QoL has become important in measuring the impact of chronic disease¹⁶. This is of particular significance as patients with the same clinical symptoms often differ in their eval uation of what the illness means to their life. The term ‘disability paradox’ is used to describe how patients with significant health and functional problems frequently have high QoL scores despite their health status³². QoL measures can be used to evaluate human and financial costs-benefits of interventions and care provided through assessing change in physical, functional, mental and social health³³.

Calman³⁴ suggests that people perceive QoL in relationship to their past experiences, current lifestyle, hopes and ambitions for the future. QoL measures the gap between the individual’s present expe rience and their expectations for the future. QoL can therefore be improved by narrowing this gap, either by improving experience or lowering expectations³⁴. Importantly, the model recognizes the highly individual nature of QoL and the influence of culture and past experience³⁵. Carr et al.³⁶ further propose a model of the relation between expectations and experience and identify three areas of dif ficulty in measuring QoL: people have different expectations; people are at different stages of their illness when QoL is measured; and expectations may change over time. By providing health education, information and increasing awareness of risks, patients are helped to adapt to their disability through changing their health expectations. The impact of the disability on their QoL may thus be reduced³⁶.

Testa and Simonson³³ recommend that measures of QoL should cover the objective and subjective components important to the rel evant patient group that may be affected positively or negatively

QoL scales should be able to demonstrate validity but this is com plicated as there is no measure of criterion validity: no scale can provide a full picture of people’s life quality or be relevant to all individuals^33,39,40. Content validity includes evaluation in terms of the applicability of the questionnaire and its comprehensiveness, as well as its clarity, simplicity and likelihood of bias⁴¹. Scales should also have predictive validity, sensitivity and be responsive to change in QoL, particularly for clinically important changes^3,33,42,43. This ensures the areas relevant to the patient’s QoL are measured and that scales are responsive to the different stages of the disease and interventions or treatment given. Orley et al.⁴⁴ argue that QoL is influenced by a broad range of facets and is therefore unlikely to alter markedly from day to day. Fallowfield⁴⁵ recommends that QoL measures should discriminate between patient groups and identify those patients experiencing good QoL and those who are not. In addition’ QoL measures used in clinical practice must be appropriate and acceptable for their intended use and the results meaningful and amenable to clinical interpretation⁴³.

Generic as opposed to disease-specific instruments offer broader measures of health status and are useful for making comparisons with other conditions’ while disease-specific instruments are used for assessing disease-related attributes when greater sensitivity to specific aspects of the clinical condition is required^3,33. Generic mea sures include single indicators’ health profiles and utility measures. Health profiles attempt to measure all aspects of health-related QoL potentially affected by a condition or its treatment. Thus generic instruments tend to be lengthy to ensure sensitivity and adequate psychometric properties³. They can be applied irrespective of the underlying condition but may be unresponsive to changes in specific conditions. Disease-specific instruments aim to have greater discrim ination between severity levels of a particular disease and thus have increased sensitivity to clinical outcomes⁴⁴. They are more concise and should be able to reflect clinically significant change in health status or disease severity. Therefore in order to detect significant clin ical changes’ generic measures may need to be supplemented with disease-specific measures¹⁶, particularly for evaluating therapeutic interventions within clinical trials³³. The use of disease-specific mea sures may’ however’ be limited as their narrow focus may not assess the impact of disease or interventions upon wider aspects of life’ which could disadvantage arguments for additional resources^24,46.

Essentially the use of both generic and disease-specific measures is recommended to ensure assessment of both disease-specific and wider aspects of life and to detect positive or negative impacts of interventions^3,16,24.

Self-Assessment Scales

The use of visual analogue scales is a common method for mea suring subjective experiences such as QoL⁴⁷. They are’ however’ time consuming to complete and may not be relevant to the experi ence being considered⁴⁵. Self-reports are obtained using standardized measures that have response formats with closed questions in a categorical dichotomous format (e.g. yes/no) or sequences of cat egorized responses (e.g. strongly agree, agree, disagree, strongly disagree). Standardized measures have fixed questions and a range of answers; Carr and Higginson³² caution that these may not measure patients’ QoL unless scores are weighted for the individual patient. Individual weightings are important for obtaining a true assessment of QoL and being responsive to change. Scores may be calculated for each domain separately or combined to provide a composite or index score of overall life satisfaction. The disadvantage of scales that are calculated to produce an overall score is that the total may result from several combinations of responses, thus leading to a loss of information about the individual components of the scale⁴⁸. Muldoon et al.¹¹ and Lawton⁴⁹ both argue that the use of a composite score fails to recognize QoL measures as being multidimensional and that it is illogical to aggregate scores that combine appraisals of objective measures of behaviour, function and subjective wellbeing; and there is a need to evaluate individual domains separately within research and clinical practice^12,30,49. Alternatively, Gill and Feinstein²⁵ advocate the use of a global rating through aggregating the scores of individual QoL domains as this explains QoL more com prehensively, and they encourage more explicit criteria or weighting of the different components that construct QoL. Furthermore global ratings have been considered more acceptable for use in clinical trials as change in QoL could be more easily distinguished.

Where self-ratings of QoL are difficult to elicit, such as in demen tia, observational ratings may be of more benefit^50-52. Observational methods are undertaken either through direct observation of the per son with dementia, which records the frequency at which certain behaviours present, or by applying attribute ratings of observed affect states over time. Direct observation is time consuming and costly but, it has been argued, provides the most objective method of rat ing QoL in dementia as the subjective component is removed^49,53