Evaluating Patient-Based Outcome Measures - NIHR Health ...

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2 Purpose and plan of this review the merits of an instrument. For example, data on the response rate associated with a questionnaire, that is, the proportion of individuals who are asked to complete a questionnaire and actually do so, may be of direct relevance to judging the acceptability of a questionnaire and ought to be relatively easy to interpret. By contrast and as the literature review in chapter 3 will demonstrate, for some of the other criteria, there are much greater inherent ambiguities and much less consensus. Thus the criterion of validity is concerned with the beguilingly simple question of whether a questionnaire is truly assessing what it purports to assess. Although there is unanimity in the literature that this is a fundamental question with patient-based outcome measures, there is no agreement on how exactly validity should be assessed. The purpose of this review is therefore to draw together the different dimensions and approaches to validity so that, ultimately, investigators can be clearer and better informed when they decide whether an instrument does have validity for a particular question addressed in a trial. It should be noted that the questions and criteria we have identified are not rank ordered in terms of importance. Nor is there any reason to think that they need to be approached in the order with which they have been presented here. Above all, in practice investigators may find they have to make trade-offs between criteria when faced with choices between instruments. For example, a questionnaire may ask such a large number of relevant questions of patients that it may appear to have considerable validity as a measure. However, its very detail and length may reduce its acceptability and feasibility. There is no evidence in the literature to assist researchers in assigning priority to the criteria we have discussed. The selection of a patient-based measure for a trial therefore remains to some extent a matter of judgement and as much an art as a science. It is our hope that the reader of this review will be clearer about the principles involved in such judgements.
The emergence of patient-based outcome measures A number of trends in health care have resulted in the development and growing use of patientbased outcome measures to assess matters such as functional status and health-related QoL (Bergner, 1985; Ebbs et al., 1989). It is increasingly recognised that traditional biomedically defined outcomes such as clinical and laboratory measures need to be complemented by measures that focus on the patient’s concerns in order to evaluate interventions and identify more appropriate forms of health care (Slevin et al., 1988). Interest in patient-based measures has been fuelled by the increased importance of chronic conditions, where the objectives of interventions are to arrest or reverse decline in function (Byrne, 1992). In the major areas of health service spending, particularly in areas such as cancer, cardiovascular, neurological and musculo–skeletal disease, interventions aim to alleviate symptoms and restore function, with major implications for QoL (de Haes and van Knippenberg, 1985; Fowlie and Berkeley, 1987; Devinsky, 1995). In many new and existing interventions, increased attention also has to be given to potentially iatrogenic effects of medical interventions in areas such as well-being and quality of life. Patient-based outcome measures provide a feasible and appropriate method for addressing the concerns of patients in the context of controlled clinical trials. At the same time, increased attention is given to patients’ preferences and wishes in relation to their health care (Till et al., 1992). Patients increasingly expect with good reason to be involved in decisions about their care and to be given accurate information to facilitate their involvement (Siegrist and Junge, 1989). More evidence, and more relevant evidence, is therefore needed by patients about how illnesses and their treatments are likely to affect them. Continuing difficulties experienced by all governments and health authorities in finding financial resources to meet demands on health care increase pressures for evidence to assess benefits in relation to costs of health care so that better use is made of resources. Evidence Chapter 2 Health Technology Assessment 1998; Vol. 2: No. 14 What are patient-based outcome measures? is needed of such benefits as perceived by patients, carers, health care professionals and by society as a whole (Epstein, 1990; Anonymous, 1991a; O’Boyle, 1995). For all these reasons, much greater effort is now required to assess the impact upon the individual of illness and treatments by means of accurate and acceptable measures. An enormous array of instruments in the form of questionnaires, interview schedules, rating and assessment forms has emerged that have in common the objective of assessing states of health and illness from the patient’s perspective. Because their purpose is to assess the impact of health care interventions from the view-point of the patient, this review refers collectively to such instruments as patient-based measures of outcome. Accompanying the mounting interest in patientbased measures is an explosion of literature. One MEDLINE search on QoL revealed 1000 articles (Rosenberg, 1995) and another retrieved three times as many QoL papers in 1994 as in 1990 (Editorial, 1995). In part, this vast and rapidly expanding literature reflects a huge growth in the number of new questionnaires and other instruments to assess health status and related concepts. In response to these developments, a number of volumes have appeared which provide guides to the different types of instruments, their content and range of applications (Wilkin et al., 1993; Bowling, 1995a; McDowell and Newell, 1996; Spilker, 1996; Bowling, 1997). These volumes provide an excellent resource for the investigator wishing to examine the range of instruments available in, for example, a particular condition such as cancer, or to assess a particular aspect of QoL such as social support. From such sources, the reader can review the range of instruments in any field and also the history of their development and use, to date. There are also now available increasingly clear and informative guidelines about how to develop and report the development of patient-based outcome measures (Sprangers et al., 1993; McDowell and Jenkinson, 1996) and how such measures should be used and reported in clinical trials (Staquet et al., 1996; Fayers et al., 1997). 3
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Professor Senga Bond, University of
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