Participants
Participants were recruited between September 2013 and March 2021. Participants of the present study were outpatients who were diagnosed with IBS in the gastroenterology and psychosomatic medicine departments of hospitals in Tokyo and Kanagawa and college students, including IBS patients or non-patient IBS who met diagnostic criteria (Rome III criteria) and those who did not meet the diagnostic criteria. The present study was approved by the ethical committee of Yokohama City University (B130905050) and the National Center of Neurology and Psychiatry (A2018-046). Written informed consent was obtained from all participants.
Measures
Cognitive Scale for Functional Bowel Disorders translated in Japanese [4]
The Cognitive Scale for Functional Bowel Disorders (CS-FBD) includes 25 items that measure maladaptive cognition related to abdominal symptoms, with responses ranging from 1 (strongly disagree) to 7 (strongly agree). The total score for this scale ranges from 25 to 175. One of the authors (N.S.), who is a psychologist knowledgeable about functional gastrointestinal disorders and psychosomatic medicine, translated the original version into Japanese. Another author (F.G.) who is bilingual in English and Japanese, back-translated the Japanese items of the CS-FBD into English. We compared the results of the back translation to the original version and confirmed agreement among the researchers about the nuances.
Japanese version of the Rome III modular questionnaire (only items related to IBS) [13,14]
The Rome III Diagnostic Criteria for Functional Gastrointestinal Disorders [15] have been widely used to define IBS. Rome IV has not been published at the start of this investigation. Using the Rome III modular questionnaire, the presence of IBS was determined if the participants had abdominal pain or discomfort for at least 3 weeks (at least once per week) in the previous 3 months and two of the three following symptoms: (1) pain or discomfort that improves or stops after a bowel movement, (2) a change in the number of bowel movements when the pain or discomfort starts, and (3) either softer or harder stools than usual when the pain or discomfort starts.
IBS Severity Index [16,17]
The IBS Severity Index (IBS-SI) was used to assess the severity of gastrointestinal symptoms. This scale consists of 5 items: abdominal pain (2 items), abdominal distension, bowel movements, and quality of life, and the total score ranges from 0 to 500. The IBS-SI classifies the severity of IBS as mild (75–174), moderate (175–299), or severe (300–500) based on clinical observations of patients with IBS.
Japanese version of Visceral Sensitivity Index [11,12]
The Visceral Sensitivity Index (VSI) is a self-reported measure of gastrointestinal symptom-specific anxiety in patients with IBS. The VSI includes 15 items with responses ranging from 1 (strongly agree) to 6 (strongly disagree), and scores ranging from 0 to 5.
Japanese version of the 24-item Dysfunctional Attitudes Scale (Tajima et al., 2007 [18])
The 24-item Dysfunctional Attitudes Scale (DAS-24) is a self-report scale for depression schemata with responses ranging from 1 (strongly disagree) to 7 (strongly agree). The DAS-24 contains three factors: “achievement,” “self-control,” and “dependency.” The achievement subscale consists of eight items, for example, “If I fail partly, it is as bad as being a complete failure.” The dependency subscale consists of eight items, for example, “I am nothing if a person I love doesn’t love me.” The self-control subscale consists of eight items, for example, “A person should do well at everything he undertakes.”
Hospital Anxiety and Depression Scale [19,20]
The Hospital Anxiety and Depression Scale (HADS) is a self-report questionnaire for anxiety and depression. The HADS includes of 14 questions on a 4-point scale, consisting of an anxiety subscale with 7 items and a depression subscale with 7 items. This psychometric instrument was chosen because all its items refer solely to an emotional state and do not consider somatic symptoms.
Procedure
Patients
Patients with IBS were given written and oral explanations about the purpose of this study, the protection of their personal information, and that participation was voluntary. Patients with IBS who agreed to participate in this study provided informed consent. Participants then completed questionnaires containing the physical and psychological scales mentioned above.
College students
The researchers recruited college students after class hours or via the university’s online bulletin board. Participants recruited by the latter method were limited to those who met the diagnostic criteria for IBS. They were given written and oral explanations about the purpose of this study, the protection of their personal information, that participation was voluntary, and that they would not be punished for not cooperating. After the above explanations were given, only those students who agreed to participate were asked to complete a series of questionnaires.
Statistical analysis
The factor structure of the CS-FBD-J was confirmed by exploratory factor analysis. Construct validity was confirmed using Pearson’s correlation coefficient analysis between the CS-FBD-J and scores on the IBS-SI, VSI, DAS, and HADS. Criterion-related validity was confirmed using one-way analysis of variance to compare the CS-FBD-J score between IBS patient group, non-patient IBS group and control group, and a post-hoc test with Scheffe’s method was employed to test the differences between groups. The internal consistency reliability of the CS-FBD-J was determined using Cronbach’s α. The correlations between each item and the total score of the CS-FBD-J were used to conduct item-total correlation analysis. The significance level was set at less than 5%. Data analyses were performed using SPSS software (version 25.0; IBM Corp., NY, USA).