SciELO - Scientific Electronic Library Online

 
vol.110 issue1Measuring health-related quality of life (HRQoL) in functional dyspepsia: is it really important?Serum thymosin beta4 as a noninvasive biomarker in patients with nonalcoholic steatohepatitis author indexsubject indexarticles search
Home Pagealphabetic serial listing  

My SciELO

Services on Demand

Journal

Article

Indicators

Related links

  • On index processCited by Google
  • Have no similar articlesSimilars in SciELO
  • On index processSimilars in Google

Share


Revista Española de Enfermedades Digestivas

Print version ISSN 1130-0108

Rev. esp. enferm. dig. vol.110 n.1 Madrid Jan. 2018

https://dx.doi.org/10.17235/reed.2017.4911/2017 

ORIGINAL PAPERS

New psychometric data from the Spanish versions of the Glasgow Dyspepsia Severity Score and the Dyspepsia-Related Health Scale measures

Miren Orive1  7  , Ane Anton-Ladislao1  7  , Nerea González1  7  , Begoña Matellanes2  , Jesús-Ángel Padierna3  7  , José-Luis Cabriada4  , Aitor Orive5  , Víctor-Manuel Orive6  , Jose-María Quintana1  7 

1Research Unit. Hospital Galdakao-Usansolo. Galdakao, Bizkaia. Spain

2Psychology Department of Personality, Psychological Assessment and Treatment. Universidad de Deusto. Bilbao, Bizkaia. Spain

3Department of Psychiatry. Hospital Galdakao-Usansolo. Galdakao, Bizkaia. Spain

4Digestive Service. Hospital Galdakao-Usansolo. Bilbao, Bizkaia. Spain

5Digestive Department. Hospital Universitario de Araba. Vitoria, Araba. Spain

6Digestive Department. Hospital Universitario de Basurto. Bilbao, Bizkaia. Spain

7Health Services Research on Chronic Patients Network (REDISSEC). Spain

ABSTRACT

Background and objective: There are no structural abnormalities in functional dyspepsia, therefore it is essential to have a viable questionnaire to measure treatment outcome according to patient perception. The aim of the study was to extensively document psychometric characteristics of the Glasgow Dyspepsia Severity Score and the Dyspepsia-Related Health Scale that are currently available in Spanish.

Methods:

Patients with functional dyspepsia (n = 158) were recruited from a randomized trial that assessed standard vs. standard and psychological treatment. Participants had completed the validation questionnaires and the Medical Outcome Study Short-form 36. Reliability (Cronbach's alpha), validity (Confirmatory Factor Analysis, convergent and known group validity) and responsiveness (minimal clinically important difference) were analyzed.

Results:

A Confirmatory Factor Analysis of the Glasgow Dyspepsia Severity Score showed a one-factor solution model, but a low Cronbach's alpha (0.61). With regard to the Dyspepsia-Related Health Scale, the Cronbach's alpha (0.80-0.97) and Confirmatory Factor Analysis supported a model with four inter-correlated dimensions and suggested a need to improve the "Satisfaction with dyspepsia-related health" dimension (Cronbach's alpha < 20). Finally, the global scores for both the Glasgow Dyspepsia Severity Score and the Dyspepsia-Related Health Scale were responsive at six months post-treatment, with a minimal clinically important difference of 4 and 6, respectively.

Conclusions:

Our findings support the continued application of the Dyspepsia-Related Health Scale and the need to improve the "Satisfaction with dyspepsia-related health" dimension. Although the Glasgow Dyspepsia Severity Score is a promising questionnaire, further review of the content is required to eliminate and add items in order to provide greater consistency to the evaluated construct.

Key words: Functional dispepsia; Psychometrics; Health-related quality of life; Factor analysis; Responsiveness

INTRODUCTION

Functional dyspepsia (FD) is a disorder characterized by the presence of recurrent symptoms of upper abdominal pain or discomfort in the absence of any known specific structural cause 1. This is the most common gastrointestinal problem seen in the primary care setting with a prevalence of 12-15% 2. This is a non-life threatening disorder and patients have a normal life expectancy however, the impact on their health-related quality of life (HRQoL) is substantial 3) (4.

Since there are no structural or biochemical abnormalities in FD, response to treatment must be assessed primarily by measuring a patients' perception about their symptoms and HRQoL via questionnaires 1) (4. However, due to the lack of validated measures this is a difficult field of research 4) (5. To the best of our knowledge, the Glasgow Dyspepsia Severity Score (GDSS) 6 and the Quality of Life in relation to Stomach and Intestinal Problems Questionnaire (QoL-PEI) 7 are the only two patient-reported outcomes measures (PROMs) available in Spanish. These have been transculturally translated and specifically created for assessing non-organic dyspeptic symptoms and their impact on a patients' daily functioning 8) (9.

In order to be considered as a viable measure of treatment outcome in clinical trials, PROMS need to be extensively documented in terms of psychometric characteristics (reliability, validity and responsiveness) in order to avoid unreliable information and bias 10. However, the GDSS is a poorly validated questionnaire and the responsiveness of the QoL-PEI has not been evaluated 6) (7) (8. For this reason, further evaluation of GDSS and DRHS is important from the perspective of regulatory issues and claims for labeling and promotion 11.

The aim of this study was to verify the psychometric characteristics and to generate more evidence with regard to the reliability (by evaluating the Cronbach's alpha), validity -by a Confirmatory Factor Analysis (CFA) and the convergent and known-group validity- and responsiveness (by evaluation of the different indexes as recommended) of the GDSS (Spanish version) and the QoL-PEI.

METHOD

Participants

Data for verifying the psychometric characteristics of the GDSS (Spanish version) and the QoL-PEI were collected as part of a parallel-group randomized controlled trial aimed at evaluating the efficacy of medical therapy plus psychotherapy among patients with FD. Both questionnaires were used to assess HRQoL after treatment in both therapeutic arms 2. Consecutive patients referred between November 2009 and September 2011 to the endoscopy units of the Galdakao-Usansolo and Basurto University Hospitals with an indication for endoscopic examination, aged between 18 and 80 years that fulfilled the ROME III diagnostic criteria for FD were included in the previous trial 12.

Patients with any organic disease that could explain the FD symptoms, the use of non-steroidal anti-inflammatory drugs (NSAIDs), physical or psychological impairments that prevented the completion of the questionnaire, or patients suffering from heartburn as the main symptom were excluded from the study. Patients with prominent FD symptoms and concomitant symptoms of irritable bowel syndrome (IBS) were not excluded, unless that they did not fulfill the ROME III criteria for IBS. Written informed consent was required in order to participate in the study. As described in greater depth in a previous paper 2, patients were randomized to receive standard medical treatment or standard medical treatment plus psychotherapy in a 1:1 ratio in blocks of 4 according to a computer generated random assignment sequence stratified by hospital site that was prepared in advance by a statistician. Patients in the control group received standard medical treatment (40 mg of an anti-secretory agent a day, 1 mg of prokinetic 3 times a day or a combination of both between 3 and 6 months). Patients in the experimental group received the same standard medical treatment plus psychotherapy based on the principles of cognitive behavioral therapy (50-minute session per week for 10 weeks, the first eight were group sessions and the last two individual sessions).

Procedure

The objective of the study was the verification of the psychometric characteristics and to obtain more evidence with regard to the GDSS (Spanish version) and the QoL-PEI. In order to achieve this, the scores of both the control and experimental groups were analyzed as a single group at baseline (T0), after 10 weeks of treatment (T1) and six months after the end of treatment (T2) via mailed questionnaires. Reminders were sent at two and four weeks to participants who had not returned their questionnaires.

The study was approved by the Ethics Committee of both participating hospitals and the study protocol conforms to the ethical guidelines of the 1975 Declaration of Helsinki (6th revision, 2008). Clinical Trials.gov Identifier: NC01802710.

Measures

Questionnaires for validation

The GDSS 13 is an eight-item self-reported dyspepsia specific questionnaire. It yields a global score that ranges from 0 to 20 and higher scores indicate more severe dyspepsia. The Spanish version of the scale 6 has a Cronbach's alpha of 0.6 and can detect differences between patient scores at inclusion with those after 6 months of follow-up.

The DRHS 14 is an eleven-item self-reported dyspepsia specific questionnaire that consists of four scales. The score for each scale ranges from 0 and 100 and 0 represents the most severe and 100 the least severe situation. The adapted and validated version of this questionnaire is known as the QoL-PEI (Quality of Life in relation to Stomach and Intestinal Problems Questionnaire) 7. The reliability of the questionnaire is satisfactory (Cronbach's alpha 0.92). A factorial analysis confirmed the four scales found by the DRHS and added a global score scale. The convergent validity measure was moderate (0.54).

Questionnaire for convergent and known-group validity analysis

The Medical Outcome Study Short-form 36 (SF-36) 15) (16 is a 36 item questionnaire that is grouped into four scales according to two different areas. The physical health area (PCS) includes physical functioning, role limitation due to physical problems, body pain and general health perceptions and the mental health area (MCS) includes role limitations due to emotional problems, vitality, general mental health and social functioning. The scores in each domain range from 0 to 100 and a score of 50 or more indicates a positive perception of health. An adapted and validated Spanish version was used in this study 17) (18 with numerous articles providing data with regard to reliability, validity and to a lesser extent, responsiveness to change 17.

A transitional question for responsiveness analysis

Patients answered the following question after psychological treatment for 10 weeks: with regard to your functional dyspepsia, how would you rate your health now compared to three months ago? The possible answers were: a) much better; b) quite a lot better; c) somewhat better; d) about the same; e) somewhat worse; f) quite a lot worse; and g) much worse. The same question was asked 6 months after the psychological treatment for patients with dyspepsia during the previous nine months.

Data analysis

The questionnaires validated in this study had 8 and 11 items. A minimum of 110 patients are required for a factor analysis according to the recommendations of Bentler and Chou 19 as the minimal number of subjects should be five or 10 times the number of observed variables.

Data were described using mean values and standard deviations (SD), frequencies and percentages. The association between socio-demographic and clinical data of the baseline questionnaires was assessed using Student's t-test or the non-parametric Wilcoxon U-test for categorical variables with two categories. The ANOVA or Kruskal-Wallis test was used for categorical variables with more than two categories and the Pearson's correlation coefficient was used for continues variables. The differences between non-responders and responders at baseline were tested using the Student's t-test or the non-parametric Wilcoxon U-test for continuous data and the Chi-squared or Fisher exact test for categorical data. In order to assess reliability, a Cronbach's alpha of at least 0.70 was used as an indicator of adequate internal consistency for both the GDSS and QoL-PEI questionnaires 20.

The structural validity was analyzed using a CFA. Based on the original questionnaires 6) (7, a one-factor solution model was tested for GDSS and a two-factor solution model in which items were divided into four inter-correlated dimensions was developed for QoL-PEI. Several adjustment indices were calculated. A value of < 2 of the ratio of the chi-squared (x2) to degrees of freedom (df), a value of the root mean square error of approximation (RMSEA) of < 0.06 and the values of the comparative fit index (CFI) and Tucker-Lewis index (TLI) of > 0.90 indicate a good model fit. Only items with a significant factor load (p < 0.05) and values > 0.40 were accepted in the final model 21.

The convergent validity was assessed by analysis of the relationship between each scale of the QoL-PEI, GDSS scale and the SF-36 (PCS) component using the Pearson's correlation coefficient (r). A negative association was expected between GDSS and the rest of the scales and a positive association between the QoL-PEI global score and the SF-36 (PCS) component.

Known-group validity was examined by comparison of the scores from the GDSS and from each QoL-PEI scale according to the SF-36 (PCS) (≤ 50 vs. > 50) and to four scales that comprised the SF-36 (PCS) component (≤ 50 vs. > 50). Patients that scored above the cut-off point of 50 on the different SF-36 subscales were expected to present lower mean values in the GDSS questionnaire and higher values for all the QoL-PEI scales. The student's t-test was used for inter-group comparisons.

To measure the responsiveness of each questionnaire, the standardized effect size (SES), standardized response mean (SRM), minimal detectable change (MDC), and minimum clinically important difference (MCID) indices were calculated. Cohen's benchmarks were used to classify the magnitude of SES and SRM indices 22. MDC was represented by the following formula: MDC = 1.96 *2* SEM, where 1.96 is derived from the 95% confidence interval of no change and 2 is included as two measurements are required to measure change 23. Finally, the MCID was estimated using the mean change score for patients who responded "somewhat better" to the transitional question. The percentage of patients that reached the threshold given by the MCID was also calculated 24. Statistical analyses were performed using SAS for Windows statistical software. All effects were considered as statistically significant at p < 0.05.

RESULTS

Patients

One hundred and fifty eight patients with FD fulfilled the inclusion criteria and completed the first survey (T0). Table 1 presents socio-demographic data, clinical characteristics and baseline scores of dyspepsia-related health of the patient group studied at T0. Within the group of patients that completed the first survey, 132 (84%) completed the questionnaires after 10 weeks of treatment (T1) and 128 (81%) completed the questionnaires at six months post-treatment (T2). According to the GDSS analysis to assess the dyspepsia related quality of life, women (p = 0.01) and/or patients taking medication (either psychiatric p < 0.001, non-prescribed medication p < 0.001 or medication prescribed by the digestive physician p < 0.001) perceive their disease as more severe. According to the QoL-PEI, patients with a poorer perceived FD related quality of life are older patients (p = 0.002), divorcees (p = 0.04) and those who take non-prescribed medication (p = 0.45).

Table 1 Sociodemographic, clinical characteristics and baseline dyspepsia-related health scores for the sample group 

a GDSS: Glasgow Dyspepsia Severity Score. This yields a global score that ranges from 0 to 20, higher scores indicate more severe dyspepsia.

b QoL-PEI: Quality of Life in relation to Stomach and Intestinal Problems Questionnaire (global score scale). This yields a global score that ranges from 0 to 100, higher scores indicate a less severe dyspepsia.

c Pearson's correlation coefficient.

FD: functional dyspepsia and x (sd): mean (standard deviation).

There were no differences between the experimental and control group at T0 and T1. At T2, non-participants were more likely to be divorced (19% vs. 3%), less educated (8% vs. 18%) and had worse baseline scores for the QoL-PEI severity of common symptoms scale (mean, 52.69 [SD, 18.04] vs. mean, 62.35 [SD, 16.89]) (data not presented).

Psychometric evaluation

  • Reliability. The Cronbach's alpha scores for GDSS were 0.61, 0.73 and 0.70 and 0.85, 0.87 and 0.88 for the QoL-PEI global score for T0, T1 and T2, respectively. The Cronbach's alpha scores for the QoL-PEI scales at T0, T1 and T2 were as follows: Severity of symptoms: 0.80, 0.82 and 0.87; pain intensity: 0.85, 0.89 and 0.85; pain disability: 0.96, 0.94 and 0.97 and satisfaction with dyspepsia health was < 0.20 for each follow-up time.

  • Structural validity. The structure of both models was supported by our data after adding various error correlations which resulted in an acceptable χ2/df (GDSS: 1.38; QoL-PEI: 1.31), CFI (GDSS: 0.96; QoL-PEI: 0.91), TLI (GDSS: 0.94; QoL-PEI: 0.90), good RMSEA (90%CI) [GDSS: 0.05 (0-0.09); QoL-PEI: 0.04 (0.02-0.06)] and good factor loadings, with the exception of the GDSS item 5 (Fig. 1) and QoL-PEI item 18 (Fig. 2). All the factor loadings were statistically significant (p < 0.001).

Fig. 1 Factor loadings in the Confirmatory factor analysis for the Glasgow Dyspepsia Severity Score (GDSS). Correlations between item 3 and 5 were performed for the GDSS error. 

Fig. 2 Factor loadings in the Quality of Life in relation to Stomach and Intestinal Problems Questionnaire (QoL-PEI). Correlations between items 6 and 8 and item 15 with pain intensity and disability scales were calculated for the QoL-PEI error. 

  • Convergent validity. Each domain of the QoL-PEI negatively correlated with the GDSS score. The bivariate correlations were moderate for Pain intensity (r = -0.52; p < 0.0001) and Global score (r = -0.54; p < 0.0001), weak for the severity of symptoms (r = -0.37; p < 0.0001) and pain disability (r = -0.47; p < 0.0001). No correlation was found for the Satisfaction with dyspepsia health scale (r = -0.19; p = 0.016). With regard to correlations between specific and general HRQoL scales, the GDSS (r = -0.35; p < 0.0001) and each domain of the QoL-PEI score correlated significantly with the standardized SF-36 (PCS). A moderate correlation was found for severity of symptoms (r = 0.50; p < 0.0001), pain disability (r = 0.53; p < 0.0001) and global score (r = 0.55; p < 0.0001). Weak correlations were found for pain intensity (r = 0.44; p < 0.0001) and no correlation was observed for the satisfaction with dyspepsia health scale (r = 0.20; p = 0.017).

  • Known-group validity. As shown in table 2, the GDSS scores decreased with an increase in the general PCS domain of the SF-36 and almost all subscales of the SF-36 physical area (except for the General health perception scale). Therefore, representing an increase in HRQoL. All scores for the QoL-PEI scales (except for the "satisfaction with dyspepsia- related health" scale) increased with an increase in the general PCS domain of the SF-36 and almost all of the sub-scales of the physical area of the SF-36 (except for the General health perception scale). Therefore, representing an increase in HRQoL.

Table 2 Known-group validity of the Glasgow Dyspepsia Severity Score (GDSS) and the Quality of Life in relation to Stomach and Intestinal Problems Questionnaire (QoL-PEI) 

SF-36: Medical Outcome Study Short-form 36; PCS: SF-36 physical component; x (sd) mean (standard deviation). aScales that belong to the PCS of the SF-36.

  • Responsiveness. Table 3 shows the responsiveness results at T1 and T2 for the GDSS and QoL-PEI. Both questionnaires showed good responsiveness data. The threshold values defined for a change that would be considered as meaningful by the patient were around 4 for the GDSS and 5 for QoL-PEI. At T2, the values were around 4 for GDSS and 6 for QoL-PEI.

Table 3 T1 and T2 responsiveness for the Glasgow Dyspepsia Severity Score (GDSS) and the Quality of Life in relation to Stomach and Intestinal Problems Questionnaire (QoL-PEI) 

DISCUSSION

The GDSS and QoL-PEI questionnaires were used to assess health-related quality of life in patients with functional dyspepsia. However, despite the information available with regard to their psychometric characteristics, some data still need to be improved 6) (7) (8. Therefore, the aim of this study was to analyze these psychometric data in a different sample in order to determine the reliability, validity and responsiveness of the questionnaires.

The article that reported the original QoL-PEI validation 14 concluded that four items be eliminated. These included "abdominal pain", "pain right now", "my abdominal discomfort interferes with my life" and "I am worried about my abdominal discomfort". However, the Spanish version 6 was translated and validated from the original questionnaire without eliminating these items. This study is based on this latter version.

With regard to reliability, the internal consistency of GDSS is not acceptable. The Cronbach's alpha value obtained in this study (0.60) was lower than the suggested level of adequacy (0.70). These findings indicate that it is unlikely that all items in the validated Spanish GDSS measure the same construct at baseline. This is consistent with the study by Fraser et al. 4, these authors noted that one of the main problems of this questionnaire is that five of the seven questions concern health-care utilization rather than symptoms or quality of life. This is a problem when a symptom-status measure is needed for cost-effectiveness trials as health-care use cannot be used in both the "cost" and "effect" dimensions 4.

With regard to the reliability of QoL-PEI's, this study found a large internal consistency for all the scales, with the exception of the Satisfaction with Dyspepsia-health scale. This observation is consistent with the cross-sectional study by Ruiz et al. 7. With regard to the last scale, Ruiz et al. 7 found an almost acceptable internal consistency (0.68) whereas this study obtained an unacceptable score (< 0.20). In accordance with the Ruiz et al. 7 and Kuykendall et al. 14 studies, we recommend avoiding questions posed in a negative way, splitting compound statements into single statements and adding items to the Satisfaction with Dyspepsia-health scale in order to improve its reliability.

In accordance with previous suggestions, a CFA was performed to support the structural validity of both the GDSS Spanish version and QoL-PEI 6) (7 questionnaires. The CFA obtained in this study confirmed the one-dimensional structure of the GDSS questionnaire and showed a good fit. However, one item had a low factor loading ("Medical home visits"), this observation could be explained by the observations found in the study by Calvet et al. 25. This study validated the Spanish GDSS performed by phone and grouped the "Medical consultations" and "Medical home visits" item into the "Consultations with a doctor because of dyspepsia" item, as home consultations are rare in this environment. With regard to the QoL-PEI, CFA performed here confirmed the two-factor solution structure in which items are divided into four inter-correlated dimensions, this was previously suggested by Ruiz et al. 7. Each four subscale may be considered independently but the questionnaire may also be used in a one-dimensional manner, thus obtaining a global score for dyspepsia-related quality of life. Due to the low factor loading, we also suggest that the "I worry about my abdominal discomfort" item be eliminated from the QoL-PEI. As mentioned above, Kuykendall et al. 14 also suggested eliminating this item.

The correlations for the convergent validity were as expected and correlations were found for all situations except for the Satisfaction with dyspepsia health scale in the QoL-PEI. On the other hand, both GDSS and QoL-PEI were able to identify differences between physical health status, physical functioning, role limitation due to physical problems and physical pain between patients (measured by different scales in the SF-36). Neither of the questionnaires differentiates patients with different general health perceptions (measured by a scale of the SF-36). This may be because these questionnaires only assess physical aspects such as symptoms or disability in relation to symptoms. Thus, the known-groups validity of the instruments was confirmed.

Finally, the fit indexes for both the GDSS and QoL-PEI global scores indicated a good responsiveness. Thus, both instruments detect small but important changes in health status over time. The MCID for the GDSS was calculated at around 4 points at T1 and T2, whereas the values for the QoL-PEI global score were calculated as around 12 points at T1 and around 6 at T2. These indices cannot be compared with the original or Spanish versions of these questionnaires as they have not yet been assessed.

Around the same time when the DRHS and GDSS were created, the Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaire was developed by Wiklund et al. 26. The psychometric characteristics of the Spanish version were documented by Kullich et al. 5, showing a good reliability (Cronbach's alpha between 0.87 and 0.95), good convergent validity and good known-group validity. Factorial analysis and responsiveness to change were not assessed. We found the following limitations in this questionnaire: a) although the assessment of symptoms has been recommended as the primary outcome for clinical trials 4, QOLRAD measures disease-specific quality of life without assessment of the frequency or severity of symptoms; b) there was a lack of useful information about the cross-cultural adaptation procedure; and c) This questionnaire does not calculate a global score.

The study described here provides a more profound analysis, particularly of the CFA and responsiveness than those reported previously. Thus responding to a need highlighted in the literature 14 and strengthening the GDSS and QoL-PEI questionnaires. The ability to assess longitudinal changes in health status is critical for the outcome measures used in the study of treatment efficacy 27. The MCID value may be the most important value to consider when evaluating a change in a patient status as this value is associated with the patient's perception of a meaningful change 28.

The present study focused exclusively on patients with functional dyspepsia that were referred to hospital, thus limiting the generalizability of the scale. Patients were not tested for H. pylori infection and a clinical assessment was not undertaken. However, these limitations allowed us to test the psychometric characteristics of both evaluated questionnaires. Another possible study limitation is the fact that data were collected as part of a parallel-group randomized controlled trial and the samples were collected from different hospitals and divided according to the treatment received. As this was not a prevalence study and clinical results were of little interest, we consider that this limitation has not interfered with the aim of the study. Finally, another limitation is that fact that we have analyzed the psychometric parameters of the QoL-PEI 7. However, these authors did not eliminate the four items proposed by the original authors 14 and also did not consider the inclusion of additional items for the Satisfaction with Dyspepsia-Related Health scale. Future research should test the psychometric characteristics of the QoL-PEI according to the suggestions by the original authors.

Our findings support a continued application of the QoL-PEI and also demonstrated its reliability, validity and responsiveness to therapeutic change for assessing functional dyspepsia-related quality of life. In addition, this study also supported its use for assessing the severity of three important dimensions of FD (symptoms, pain intensity and disability). Further research with this scale is encouraged, especially with regard to the improvement of the Satisfaction with Dyspepsia-related health dimension. Although the GDSS is a promising questionnaire for assessing the impact of functional dyspepsia symptoms, it does not measure functional dyspepsia-related quality of life. In addition, further review of the item content is required and some items should be eliminated and added in order to provide a greater consistency to the construct evaluated.

ACKNOWLEDGMENTS

We are grateful to all the members of the Department of Gastroenterology from the Galdakao-Usansolo and Basurto University Hospitals. Especially the endoscopy experts (Drs. M. Lorenzo, J. Aguirre, J. Cabriada, M. López, M. González, M. Durán, A. Bernal, J. Arevalo, A. Hernández, L. Bridet) and Dr. J. Hernández and Dr. San Salvador (a specialist from the Bilbao region's primary care service) for their invaluable collaboration in patient recruitment. We are also grateful to Amaia Navarro for help with the psychotherapy treatments, the participants who took part in this study and the Research Committee of the Galdakao-Usansolo Hospital.

This work was supported by a grant from Department of Health of the Basque Country (2008111005).

REFERENCES

1. El-Serag HB, Talley NJ. Systematic review: health-related quality of life in functional dyspepsia. Aliment Pharmacol Ther 2003;18:387-93. DOI: 10.1046/j.1365-2036.2003.01706.x [ Links ]

2. Orive M, Barrio I, Orive VM, et al. A randomized controlled trial of a 10 week group psychotherapeutic treatment added to standard medical treatment in patients with functional dyspepsia. J Psychosom Res 2015;78:563-8. DOI: 10.1016/j.jpsychores.2015.03.003 [ Links ]

3. Ford AC, Moayyedi P. Dyspepsia. Curr Opin Gastroenterol 2013;29:662-8. DOI: 10.1097/MOG.0b013e328365d45d [ Links ]

4. Fraser A, Delaney B, Moayyedi P. Symptom-based outcome measures for dyspepsia and GERD trials: a systematic review. Am J Gastroenterol 2005;100:442-52. DOI: 10.1111/j.1572-0241.2005.40122.x [ Links ]

5. Kulich KR, Madisch A, Pacini F, et al. Reliability and validity of the Gastrointestinal Symptom Rating Scale (GSRS) and Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaire in dyspepsia: a six-country study. Health Qual Life Outcomes 2008;6:12. DOI: 10.1186/1477-7525-6-12 [ Links ]

6. Mones J, Adan A, Lopez JS, et al. Validation of the Spanish version of the Glasgow Dyspepsia Severity Score. Rev Esp Enferm Dig 2001; 93:164-175. [ Links ]

7. Ruiz M, Villasante F, Leon F, et al. Dyspepsia-related quality of life. Spanish adaptation and validation of the questionnaire Dyspepsia-Related Health Scale. Med Clin (Barc) 2001;117:567-73. DOI: 10.1016/S0025-7753(01) 72182-3 [ Links ]

8. Badia X, Alonso J. La medida de la salud. Guía de escalas de medición en español. Barcelona: Fundación Lilly; 2007. [ Links ]

9. Jorda F, Vivancos J. Evaluación de la calidad de vida en las enfermedades digestivas. Gastroenterol Hepatol 2004;27:26-36. [ Links ]

10. Shah HA, Dritsaki M, Pink J, et al. Psychometric properties of Patient Reported Outcome Measures (PROMs) in patients diagnosed with Acute Respiratory Distress Syndrome (ARDS). Health Qual Life Outcomes 2016;14:15. DOI: 10.1186/s12955-016-0417-7 [ Links ]

11. Kulich KR, Wiklund I, Junghard O. Factor structure of the Quality of Life in Reflux and Dyspepsia (QOLRAD) questionnaire evaluated in patients with heartburn predominant reflux disease. Qual Life Res 2003;12:699-708. DOI: 10.1023/A:1025192100450 [ Links ]

12. Drossman DA, Dumitrascu DL. Rome III: New standard for functional gastrointestinal disorders. J Gastrointestin Liver Dis 2006;15:237-41. [ Links ]

13. el-Omar EM, Banerjee S, Wirz A, et al. The Glasgow Dyspepsia Severity Score--a tool for the global measurement of dyspepsia. Eur J Gastroenterol Hepatol 1996;8:967-71. DOI: 10.1097/00042737-199610000-00006 [ Links ]

14. Kuykendall DH, Rabeneck L, Campbell CJ, et al. Dyspepsia: how should we measure it? J Clin Epidemiol 1998;51:99-106. [ Links ]

15. McHorney CA, Ware JE, Raczek AE. The MOS 36-Item Short-Form Health Survey (SF-36): II. Psychometric and clinical tests of validity in measuring physical and mental health constructs. Med Care 1993;31:247-63. DOI: 10.1097/00005650-199303000-00006 [ Links ]

16. Ware JE, Sherbourne CD. The MOS 36-item short-form health survey (SF-36). I. Conceptual framework and item selection. Med Care 1992;30:473-83. DOI: 10.1097/00005650-199206000-00002 [ Links ]

17. Vilagut G, Ferrer M, Rajmil L, et al. The Spanish version of the Short Form 36 Health Survey: a decade of experience and new developments. Gac Sanit 2005;19:135-150. DOI: 10.1157/13074369 [ Links ]

18. Vilagut G, Valderas JM, Ferrer M, et al. Interpretation of SF-36 and SF-12 questionnaires in Spain: physical and mental components. Med Clin (Barc) 2008;130:726-35. DOI: 10.1157/13121076 [ Links ]

19. Bentler PM, Chou CH. Practical issues in structural modeling. Sociological Methods & Research 1987;16:78-117. DOI: 10.1177/0049124187016 001004 [ Links ]

20. Cronbach LJ. Coefficient alpha and the internal structure of test. Psychometrika 1951;16:297-334. DOI: 10.1007/BF02310555 [ Links ]

21. Hatcher L. Developing measurement models with Confirmatory Factor Analysis. A step by step approach to using the SAS system for factor analysis and structural equation modelling. North Carolina: SAS Institute; 1994. pp. 249-342. [ Links ]

22. Cohen J. Statistical power analysis for the behabioral sciences. New Jersey: Lawrence Erlbaum Associates; 1988. [ Links ]

23. de Vet HC, Terwee CB, Ostelo RW, et al. Minimal changes in health status questionnaires: distinction between minimally detectable change and minimally important change. Health Qual Life Outcomes 2006;4:54. DOI: 10.1186/1477-7525-4-54 [ Links ]

24. Copay AG, Subach BR, Glassman SD, et al. Understanding the minimum clinically important difference: a review of concepts and methods. Spine J 2007;7:541-6. DOI: 10.1016/j.spinee.2007.01.008 [ Links ]

25. Calvet X, Bustamante E, Montserrat A, et al. Validation of phone interview for follow-up in clinical trials on dyspepsia: evaluation of the Glasgow Dyspepsia Severity Score and a Likert-scale symptoms test. Eur J Gastroenterol Hepatol 2000;12:949-53. DOI: 10.1097/00042737-200012080-00016 [ Links ]

26. Wiklund IK, Junghard O, Grace E, et al. Quality of Life in Reflux and Dyspepsia patients. Psychometric documentation of a new disease-specific questionnaire (QOLRAD). Eur J Surg Suppl 1998;41-9. DOI: 10.1016/S0016-5085(98)80199-6 [ Links ]

27. Schmitt JS, Di Fabio RP. Reliable change and minimum important difference (MID) proportions facilitated group responsiveness comparisons using individual threshold criteria. J Clin Epidemiol 2004;57:1008-18. DOI: 10.1016/j.jclinepi.2004.02.007 [ Links ]

28. Michener LA, McClure PW, Sennett BJ. American Shoulder and Elbow Surgeons Standardized Shoulder Assessment Form, patient self-report section: reliability, validity, and responsiveness. J Shoulder Elbow Surg 2002;11:587-94. DOI: 10.1067/mse.2002.127096 [ Links ]

Received: March 14, 2017; Accepted: September 14, 2017

Correspondence: Miren Orive. Research Unit. Hospital Galdakao-Usansolo. Barrio Labeaga, s/n. 48960 Bizkaia, Spain. e-mail: miren.orivecalzada@osakidetza.eus

Creative Commons License This is an open-access article distributed under the terms of the Creative Commons Attribution License