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See article on page 527
Functional bowel disorders are highly prevalent in the general population. In the US Householder Survey about 70% of respondents had at least one functional bowel disorder, 9.4% had irritable bowel syndrome (IBS) and 2.9% had functional dyspepsia.1 These disorders often have significant symptom overlap making them difficult to distinguish.2 3 In this issue (see page 527), Chassanyet al describe the initial development, preliminary psychometric testing and cross-cultural assessment of a multi-item disease specific health related quality of life (HRQOL) instrument for use in multinational clinical trials of IBS or functional dyspepsia. If only an efficacious therapy could be found!
Health related quality of life assessment is becoming increasingly recognised as an important outcome and predictor for patients with chronic diseases. HRQOL is generally assessed by quantitative questionnaires completed by patients themselves which assess physical and psychosocial attitudes and function. The three kinds of HRQOL measures used in research and practice include global assessments, generic instruments and disease specific instruments.4 5The global assessment, usually a graded summary such as good, fair or poor or a 10 cm visual analog scale, may help to predict a relation between simple parameters, like disease severity and function, but is often inadequate for more sophisticated hypothesis testing. Generic instruments are multi-item problem lists that are meant to be independent of sex, age and disease and are applied to compare different populations or diseases. Items are frequently clustered in subscores, such as “physical” or “emotional function”, “somatic sensation” or “mental health”, or may be summarised into a single score. These can identify unexpected factors affecting HRQOL and may also be useful in predicting health outcome. Disease specific instruments are used to detect important treatment effects or changes with time. They are also multi-item inventories that have been derived in patients with a single condition. Most studies now combine generic and disease specific instruments to optimise the ability to detect important HRQOL changes and to avoid missing unexpected effects.4 5
Before using an HRQOL index, it must undergo psychometric assessment of validity, reliability, and responsiveness.4-7 Validity is a comparison of the new index score and a reference score (convergent validity) or a construct of what the new index is measuring, such as a prediction that patients with more severe disease will have poorer HRQOL scores (construct validity).4 5 “Reliability” is an assessment of the measurement error of scores or correlations among items or subscores.6 “Responsiveness” gives a signal-to-noise ratio and allows interpretation of what degree of change is clinically important.8
The FDDQL developed by Chassany and colleagues passed through four stages: item selection, test−retest reliability evaluation, therapeutic trials, and cross-cultural validation (French, English, German). The final questionnaire of 43 items has responses graded on a five point scale and aggregated into eight subscales [daily activities, anxiety, diet, sleep, discomfort, coping with disease, control of disease, stress], seven of these summed in a global score (excluding stress). Scores range from 0 to 100, with a higher score representing better HRQOL. Validity was confirmed by showing that:
Mean scores in functional dyspepsia or IBS were similar among countries. Spearman correlations of FDDQL and SF-36 subscales ranged from 0.41 to 0.69 (convergent validity).
Mean scores, stratified by the number of gut symptoms present (discriminant validity), gave progressively lower scores.
Item to subscale Pearson correlations (structure confirmation) were r > 0.4.
Mean scores among five subgroups (graded by the investigator from no handicap to severe handicap) demonstrated increasingly poor HRQOL.
Test–retest reliability of the final instrument will need to be re-evaluated as there have been three iterations since the first questionnaire. Internal consistency, as measured by Cronbach’s alpha of 0.94, was excellent. Sensitivity to detect change over time was not assessed and will need to be undertaken during a clinical trial.
Since this study was initiated, two other disease specific IBS HRQOL instruments have been described.8 9 The IBSQOL of Hahnet al has 30 items, nine subscales, with responses of five or six grades, each score of 0 to 100 (higher score better HRQOL).8 Scores could significantly distinguish patients with non-IBS gut disorders from two referred groups with IBS and internal consistency was as good as the FDDQL with alphas of 0.66 to 0.93. The IBS-QOL, the second questionnaire (note the hyphen), is probably the most extensively validated of the three instruments.9 This index has 34 items, eight subscales, item responses are graded on a five point scale, total score 0 to 100 with a higher score indicating poorer HRQOL. Internal consistency was 0.74 to 0.95 and test–retest reliability intraclass correlations were 0.65 to 0.89. Comparisons with other instruments (subscales of SF-36, Psychological General Well Being Index, SCL90-R) gave moderater values of 0.30 to 0.47, supporting the convergent validity. As the frequency and severity of symptoms increased, IBS-QOL scores deteriorated significantly. This instrument, in contrast to the FDDQL, did correlate moderately with pain and also with absenteeism from work. The IBS-QOL has also undergone some cross-cultural validation.
None of these three instruments has yet been assessed for ability to reflect important clinical changes (responsiveness). There is an unsurprising degree of similarity in questions, responses, subscales, and scoring techniques. Even the consistency, reliability coefficients and validation correlations are of a similar magnitude. The FDDQL is somewhat different from the other two IBS indexes in that it seems to incorporate some problems specific to functional dyspepsia and with further validation it will become clear how valuable it can be for this disorder.
The appropriate clinical trial is needed not only for clinicians who wish to improve the HRQOL of these patients, but also to assess the value of these instruments. In such a clinical trial, it will be important to study only one functional bowel disorder, IBS, and other outcomes will be essential, such as disease severity scores, pathophysiology and mechanism of treatment.
Both generic and disease specific HRQOL instruments should be combined to determine which are clinically important changes and to avoid missing unexpected associations. Adjustment of scores should be undertaken for disease severity, and sex and age differences should be explored further. The authors might also consider the study by Eypaschet al who devised a general Gastrointestinal Quality of Life Index (GIQLI), with a group of core items and additional modules for more specific diseases.10 Their final questionnaire has five domains, 32 items, graded responses (0 to 4) and a sumscore of 0 to 128 (a higher score denoting better HRQOL). It was tested for face validity and reliability (ICC 0.92), and was shown to be responsive in 194 patients who had laparoscopic cholecystectomy. Scores improved significantly (p<0.001) from a mean (SD) of 87.3 (17.25) to 104.5 (17.52) two weeks after surgery. Would it not be wise to consider collaborative efforts among international groups, to expedite full validation of instruments, avoid redundancy and develop more instruments with broader applications for which cross-cultural validation could be hastened. A plea for HQQLI (High quality quality of life instruments).
See article on page 527
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