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Health-related quality of life refers to how disease impacts on those areas of life that make it worth living, including physical and emotional functioning.1 Substantially reduced quality of life has recently been documented in patients with functional dyspepsia.2–7 However, earlier studies primarily applied non-specific quality of life instruments, such as the short form-36 (SF-36) or the Psychological General Well-Being Index, which contain multiple items, many of which may be irrelevant to dyspepsia.1, 8–10
Only recently has serious attention been given to developing accurate symptom and quality-of-life outcome measures in functional dyspepsia.8, 9 In clinical trials, quality of life is often considered as a secondary outcome to symptom relief, but there is increasing interest in considering quality-of-life improvement as a primary objective of therapy in conditions such as functional dyspepsia, which cause no mortality.8, 9 However, there would be no value in assessing quality of life if the symptom measures cover essentially the same patient concerns. In functional dyspepsia, this has been a little-studied area.
A self-report disease specific questionnaire for functional dyspepsia, the Nepean Dyspepsia Index, has been developed to measure both symptom status and quality of life.3, 4 In previous studies, we have demonstrated that the 42-item Nepean Dyspepsia Index quality-of-life questionnaire appeared to be reliable and accurate. It could also discriminate dyspepsia from health in uninvestigated patients with dyspepsia recruited from family practice in Australia and in a random population sample from New Zealand.3 The Nepean Dyspepsia Index had four sub-scales identified originally. A subsequent study of 101 US patients with functional dyspepsia showed that the Nepean Dyspepsia Index could be shortened to 25 quality-of-life items with five sub-scales; the revised instrument remained reliable and valid.4 Its ability to measure change (i.e. responsiveness) was assessed but not in the setting of a large randomized controlled trial; the initial responsiveness data were encouraging but not definitive.4
The aim of this study was to develop an even briefer, easy to score self-report measure that reliably and validly measures symptoms and quality of life in functional dyspepsia, and is sensitive to change in clinical status. We also wished to determine whether symptom assessment alone is adequate in clinical trials to capture the impact of functional dyspepsia. We therefore applied the Nepean Dyspepsia Index in a large multicentre trial in Europe and the United States, which provided an opportunity to prospectively test the instrument in functional dyspepsia.
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While dyspepsia is a recognized major health problem in the community, probably costing billions annually in the United States, treatment remains unsatisfactory.13 When testing new therapies, validated measures of outcome are needed which are responsive to change, yet these have been largely unavailable.3 The Rome II Working Teams have recommended the use of validated quality-of-life instruments in clinical trials of patients with functional gastrointestinal disorders, especially when such instruments have been shown to be able to detect change.14 Generic instruments are unlikely to be as useful as a disease-specific measure for quantifying changes in impaired quality of life in functional dyspepsia with therapy.15 The lack of availability of a disease specific quality-of-life measure for functional dyspepsia has, in the past, limited the options for researchers.16
The Nepean Dyspepsia Index questionnaire described in this study is actually composed of two distinct, separately scored and interpreted instruments: a symptom checklist and a disease specific quality-of-life measure. The former is made up of a list of common upper gastrointestinal symptoms which respondents rate in terms of three dimensions, whilst the full Nepean Dyspepsia Index quality-of-life section is composed of 25 items which include disease impact items and an importance rating.4 A measurement instrument is valid if the information recorded corresponds to the true state of affairs.17 For this to be the case, the instrument must be reliable; hence repeated measurements should fall closely to each other assuming the situation is stable.17 We have previously shown that the full version of the Nepean Dyspepsia Index was reliable on two distinct occasions by test–retest and had high internal consistency. In the present study, we confirmed the internal consistency of the long form and found that the short 10-item version also had high internal consistency. Hence, we conclude that the Nepean Dyspepsia Index has excellent reliability across various study populations.
However, reliability alone does not necessarily establish validity; an instrument may reliably measure concepts that are systematically missing the mark.17 Because no gold standard exists to establish the validity of a quality-of-life measure, determining an instrument’s validity requires a number of steps. We have previously established that the full Nepean Dyspepsia Index quality-of-life items measure relevant areas of life in patients with functional dyspepsia (i.e. the instrument has face and content validity) and the long form Nepean Dyspepsia Index discriminates patients with uninvestigated dyspepsia from healthy subjects (discriminant validity).3, 4 Furthermore, the instrument measures concepts that are linked to but are not covered by the symptom evaluation.4 Importantly, in the present study we confirmed that symptom items did not adequately explain the quality-of-life domains captured by the Nepean Dyspepsia Index. Similarly, we have previously reported that the SF-36 (a well-established generic quality-of-life measure) correlated with the Nepean Dyspepsia Index, and anxiety and depression also correlated with the Nepean Dyspepsia Index, but none of these measures alone or combined could replace the Nepean Dyspepsia Index (convergent validity).4 It therefore appears that the Nepean Dyspepsia Index can be usefully and confidently applied in studies of functional dyspepsia.
A potential omission with all previous quality-of-life instruments in gastroenterology has been the lack of weighting of items relating to the relative importance to each individual.1 In individuals, certain activities that really matter to that person are likely to be more affected by an illness. Theoretically, weighting the importance of domains could improve the performance of an instrument. In our original report, rating of importance in the Nepean Dyspepsia Index was not of additional discriminatory value.3 While we have subsequently shown that weighting may be of some relevance, it appears not to be essential, based on the present results.4 We found that the originally constructed quality-of-life instrument could be further simplified into five two-item sub-scales, with a total of just 10 items. Applying individual weights from the original groups of items was not required, based on the psychometric testing performed.
In previous work, initial data on responsiveness were also gathered but only a 2-week period was measured.4 While the data suggested that the instrument was at least modestly responsive, as there was no specific intervention tested in this study, large changes were not expected. For this reason, we set out to test the Nepean Dyspepsia Index in a large clinical trial, to determine its level of responsiveness and set the scene for future work. We found that symptoms and quality of life significantly changed from baseline in parallel in the present trial. Concordant with the independent symptom measures, large changes were observed in the placebo and active therapy groups. We assessed the standardized response mean to document sensitivity to change; similar, high responsiveness scores for both the full and short versions of the Nepean Dyspepsia Index were observed. Hence, we now have available a very brief, valid disease-specific quality-of-life measure that can be applied in clinical trials of functional dyspepsia. A strength of the study is that we did include a wide range of patients from multiple countries in this trial, and hence the results should be broadly generalizable.
There are few other disease-specific quality-of-life measures available for dyspepsia. Rabeneck and colleagues reported the development of the SODA (severity of dyspepsia assessment).18 However, this is a complex instrument to score and does not measure quality of life but rather symptoms and satisfaction. Furthermore, its responsiveness is not established and the generalizability outside of males in a Veterans Administration (VA) hospital setting needs to be determined. An international research group has independently developed the quality of life in reflux and dyspepsia (QOLRAD) questionnaire.19 This instrument is psychometrically sound; it contains 25 items measuring emotions, vitality, sleep, diet and physical/social functioning, and is very responsive to change in GERD.20 On the other hand, a distinction between dyspepsia and reflux was not a goal of instrument development and its responsiveness in functional dyspepsia is uncertain. The Gastrointestinal Symptom Rating Scale (GSRS) is a valuable symptom measure but it is not specific for dyspepsia and does not assess quality of life.21 McColl and co-workers have developed the Glasgow Dyspepsia Severity Score.22 Rather than a comprehensive disease-specific quality-of-life measure, the Glasgow scale is an investigator-based global measure of dyspepsia (which is not defined in the instrument); specific symptom items are not assessed. It also asks about the global effect on routine activities, time off work, consultations, tests and medications, and importantly is relatively brief and responsive. However, a disadvantage of the Glasgow scale is its reliance on the investigator (and his or her definition of dyspepsia, which is likely to not be standardized). A study from Ireland has also reported the validation of a new dyspepsia measure, but it only measures four symptoms and the validity remains to be adequately established.23 A study from the US reported excellent psychometrics for the Digestive Health Status Instrument (DHSI), but this is not a quality-of-life measure.24
In conclusion, we have developed a valid multidimensional disease-specific quality-of-life measure that was highly responsive to change in a clinical trial. The available results suggest that the short form Nepean Dyspepsia Index will be useful in future clinical trials of dyspepsia and functional dyspepsia.