Background
Irritable bowel syndrome (IBS) is diagnosed on the basis of recurrent abdominal pain related to defecation or changes in stool frequency or form [
1,
2]. The current prevalence of IBS ranges from 2.5 to 25%, depending on the diagnostic criteria used [
3,
4]. For instance, the Manning criteria are associated with considerably higher prevalence rates when compared to the Rome I-III criteria. The prevalence of IBS is higher in women than in men. However, these gender differences decrease with increasing age [
5,
6].
Patients with IBS experience a great degree of stress as a result of the condition. Several investigations with heterogeneous patient samples have illustrated that quality of life is perceived as being significantly impaired [
7‐
10]. Further, adolescents suffering from IBS report a lower quality of life [
11]. Moreover, IBS patients show considerably reduced health-related quality of life on all scales of the Short Form Health Survey (SF-36) [
12] compared to other patient groups such as those with heart insufficiency [
13]. A recent cross-sectional study from Norway has shown that IBS is associated with poor outcomes, particularly in the presence of health complaints, organic diseases, and affective disorders [
14].
Three validated scales are available to assess IBS severity, of which the IBS severity scoring system (IBS-SSS) is most frequently used [
15]. However, the IBS-SSS is an external assessment tool which has to be administered by the treating physician.
Häuser [
16] has produced a German translation of the Rome III criteria for IBS that allows for a categorical decision about the presence of IBS. However, none of these tools include a patient self-assessment which would provide valuable additional information to the external assessment, particularly with regard to the disruptions in quality of life frequently occuring [
9,
17]. The validated Gastrointestinal Symptom Rating Scale for Irritable Bowel Syndrome (GSRS-IBS) by Wiklund et al. [
18] firstly represents such a diagnostic tool, which is currently only available in the English language.
The instrument was first introduced in 2003 with the aim to establish a self-assessment tool specifically adapted to IBS patients [
18]. The GSRS-IBS is based on the Gastrointestinal Symptom Rating Scale (GSRS-IBS, [
19]) developed for IBS patients and the Health-Related Quality of Life Questionnaire (HRQL, [
20]) which is disease independent.
Currently, there is no appropriate questionnaire available in the German language (spoken by approximately 100 million people) to assess self-perceived symptom severity in IBS. However, such an assessment tool would be useful in the context of clinical practice as it would aid formation of a diagnosis and the monitoring of the course of IBS and additionally, for clinical studies.
Objectives
Therefore, the aim of this study was to develop a German version of the GSRS-IBS (in the following called Reizdarm-Fragebogen, RDF) and to carry out a cross-cultural validation. For this purpose, the original questionnaire was translated into German and, in accordance with Wiklund et al. [
18], was subsequently validated in a sample of IBS patients. Moreover, control groups were included to evaluate the
specificity of the questionnaire.
Methods
The purpose of the following section is to provide a brief overview of the translation and design process of the German version of GSRS-IBS and to describe its validation in a sample of different subgroups.
Design of the German instrument
GSRS-IBS
The English version GSRS-IBS includes 13 items, which are rated on a seven-point scale ranging from "1 = no discomfort at all" to "7 = very severe discomfort". All items exclusively capture IBS constructs. The questionnaire was neither designed to produce ceiling effects nor to assess redundant information. A factor-analytical examination of all items in a validation cohort provided the following five factors: pain, diarrhoea, satiety, constipation, and bloating. Based on these findings identically named subscales containing two to four items were defined and demonstrated satisfactory internal consistencies reflected in Cronbach’s Alpha (α) ranging from .74 to .85.
Translation
In order to ensure a high quality translation process, a series of standards exists specifically for the cross-cultural translation of
psychological and medical questionnaires [
21]. The translation of the GSRS-IBS into German (RDF) was conducted in accordance with these recommended procedures. A preliminary version of the questionnaire was subsequently tested in a clinical sample. Contrary to the recommended standard specifications, no committee of experts was consulted concerning the quality of the questionnaire. Nonetheless, experienced gastroenterologists (including FL) confirmed its validity.
With regard to the specific process, two translators possessing the necessary knowledge of English and medical expertise independently translated the original questionnaire into their native German language. Both translations were then compared and the language was fine-tuned, which resulted in the translators agreeing on one version of the questionnaire. In order to assure the quality of the translation, the new version was retranslated back to English by two native English speakers who were not familiar with the original text. Except for some different choice of wording, the original English text did not differ from the retranslated version of the questionnaire, thus confirming the accuracy of the initial translation of the GSRS-IBS into German. Subsequently, the newly generated version of the questionnaire was given to a group of patients in a psychosomatic rehabilitation clinic in Blieskastel (MediClin Biestal-Kliniken), who were asked to check the comprehensibility of the items. None of these patients reported problems with comprehension. Therefore the German version was considered ready for implementation in the following validation study.
Study process
Study procedure and instruments
Statistical analyses
Initially, according to Wiklund et al. [
18] a total score of the RDF as well as the individual sub-scores for the five proposed subscales in the English version were calculated for each subject by summing the total of the 13 items. Moreover, sum scores were calculated for the identified subscales in the German version following the outcome of a subsequent factor analysis. Regarding both, the GBB-24 and the HADS-D, scoring was carried out according to the respective manual instructions. A total score as well as scores for the proposed subscales were calculated for the GBB-24. Additionally, a total score for anxiety and depression symptoms was calculated for the HADS-D. In case of missing data for a maximum of two of the 13 RDF items, the missing values were replaced by the subject's mean score. If three or more answers were missing, the subject was excluded from all analyses. The same principle was applied to the HADS-D and the GBB-24. However, in case of the latter a subject was excluded from analyses if five items or more were missing.
A new variable was created to compare presence versus absence of IBS. Thereafter, a binary logistic regression was calculated in order to verify if the IBS patients could be distinguished from the other groups based on their RDF results.
Internal consistencies (Cronbach’s Alpha, α, [
26]) were calculated for the entire questionnaire and for the subscales identified in the German version of the questionnaire, to determine the reliability of the RDF. Furthermore, the item difficulties and the item-total correlations were evaluated in order to assess item quality. To identify the factorial structure of the questionnaire, in comparison to the English validation, a slightly different procedure was employed: An exploratory principal axis analysis was performed with an oblique (Direct oblimin, Delta = 0) rotation. This analysis was chosen since exploratory factor analyses only consider item variance which is shared by at least two items. This was deemed to be more appropriate regarding measurement error [
27]. Additionally, an oblique rotation appears to be more reasonable concerning the nature of IBS symptoms with respect to the chosen orthogonal rotation from Wiklund et al. [
18]. To assume that those who suffer from severe constipation perceive the same amount of pain as those who do not suffer from constipation is implausible, which is why it seems appropriate to permit intercorrelations between factors.
The factor analyses were performed for the entire sample as well as separately for the subgroups (IBS, IBD, psychosomatic patients and control groups). Consequently, there is a factorial structure analysis for the entire sample (n = 372) from which 83% did not have a diagnosis of IBS. This can subsequently be compared to the factorial structure analysis in 65 patients with IBS. Moreover, this analysis in the IBS subsample can be compared with the IBS sample that was recruited for the validation of the original English version of the questionnaire. However, this comparison is limited due to the different types of factor analysis. Correlations with the GBB-24, its subscales and the HADS-scores were calculated to illustrate the questionnaire's convergent construct validity.
Discussion
The results suggest that the RDF as the German version of the GSRS-IBS, can be used as a reliable and valid questionnaire to assess self-perceived severity and to monitor progress in IBS patients in German-speaking countries. The present analyses establish the RDF as a reliable and economical tool. This is evidenced by the sufficient psychometric quality of the tests, its plausible, factorial structure as well as its selective sensitivity for IBS symptoms. In line with this, significant differences in the total RDF score were reported for IBS patients in comparison to other clinical and non-clinical samples. Its suitability is further reflected by the convergent validity apparent in the correlations between the RDF and the GBB-24 and the HADS-D. The present study further demonstrates that the German version of the RDF is also suitable for subjective severity assessment of IBS and that the same IBS construct is consequently acquired in the English-speaking world as well as in Germany [
29].
However, it must be noted that the factorial structure of the German version does not perfectly match the original English version. The method of choice to prove the similarity of the factorial structure would certainly have to be a confirmatory factor analysis [
30]. This method was deliberately not applied in the present study due to methodological reasons. A different exploratory approach was chosen that, on the one hand, seems to be more appropriate for the data - with respect to the inter-factor correlations and the considered variances - but, on the other hand, distinctly limits the comparison of the findings with the results from Wiklund et al. [
18]. The employed factorial analysis resulted in four instead of five factors and raises concerns over whether the five-factorial structure found in the English original and the associated interpretation of the scales should be adjusted. It may be advisable to initially focus on the value of the entire RDF and to subsequently define the exact scale structure and compile indications of its interpretation, only after a further validation sample.
Despite the scale structure that still needs to be investigated, the RDF can certainly be recommended for its application in a screening procedure. However, in order to ensure a meaningful implementation in daily clinical practice or in general practitioner practices, it would be reasonable to define cut-off-values. This would require a larger sample of IBS patients, which would also be necessary to determine the extent to which the questionnaire is suitable to assess the subjective and additionally the objective degree of IBS. A comparison with the currently used severity scores in daily clinical practice would be particularly important. Such a comparison would also establish to what extent the RDF can be meaningfully implemented to document the (subjective) progression of IBS and if it should be included in the standard therapy plan.
Limitations
On a critical note, only 65 patients with IBS were recruited for this investigation, a small sample compared to the 234 IBS patients used in the validation of the original English version. This relatively small sample size is especially associated with limitations in the interpretation of the factorial analytical results. Smaller samples (and thus samples with a greater range restriction) are more likely to be associated with a larger number of factors, which could present an alternative explanation for the diverse factorial structures in the total cohort and in the group of IBS patients. The fact that the IBS patients were less suitable for the factor analytic investigation is reflected in the significantly lower KMO coefficients, even when compared to the entire sample. Moreover, the control group comprising students is a further limitation, as characteristics such as age, years of education and socioeconomic status differed in the two groups, thus limiting their comparability. However, the inclusion of orthopaedic patients should have reduced such influences. Nevertheless, a replication and expansion of this study with a larger patient cohort and a matched control group would be desirable.
Additionally, not all aspects of the test quality could be taken in consideration. For instance, findings regarding stability of the results in terms of retest-reliability are lacking. The coherence of the HADS-D and the GBB-24 point towards a persuasive convergent construct validity, while a proof of a sufficient discriminant validity is indeed missing. Likewise, it seems reasonable to examine the extent to which the RDF scores correlate with other relevant variables within IBS.
Conclusion
The German version of the GSRS-IBS RDF proves to be an effective, reliable, and valid questionnaire for the assessment of self-perceived symptom severity in IBS, which can be used in clinical practice as well as in clinical studies.
Acknowledgements
We would like to sincerely thank Dr. Jutta Besch, who supported this project by helping us to recruit patients with IBS from her internal medicine practice in Neunkirchen. Further, we thank Marlene Staginnus for helping proof reading the manuscript.
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