2.2.1. Baseline data collection

We collected baseline demographic data and asked respondents to state whether they had seen a primary care physician or a gastroenterologist about their gastrointestinal symptoms. We captured lower gastrointestinal symptom data at baseline using the Rome IV questionnaire. ²⁰ Among those individuals who did not meet the Rome IV criteria for IBS at baseline, we used the scoring algorithms proposed for use with the Rome IV questionnaire to assign presence or absence of the four other Rome IV‐defined functional bowel disorders. We measured the impact of gastrointestinal symptoms at baseline in terms of the proportion of time that they limited normal daily activities, according to the Rome IV questionnaire, ²⁰ and dichotomized this at a threshold of interference with daily activities ≥50% of the time.

We collected anxiety and depression data via the hospital anxiety and depression scale (HADS), ²¹ with a total score ranging from a minimum of 0 to a maximum of 21 for either anxiety or depression. A score ≤7 is considered normal, 8–10 borderline abnormal, and ≥11 abnormal. We collected extra‐intestinal symptom data via the patient health questionnaire‐12 (PHQ‐12), ²² derived from the validated PHQ‐15. ²³  The total PHQ‐12 score ranges from a minimum of 0 to a maximum of 24. We categorized severity into high (total PHQ‐12 ≥13), medium (8–12), low (4–7), or minimal (≤3).

We utilized the 15‐item visceral sensitivity index (VSI), ²⁴ which measures gastrointestinal symptom‐specific anxiety. Replies to each item are provided on a six‐point scale from “strongly disagree” (scored as 0) to “strongly agree” (scored as 5). There are no validated cut offs to define levels of gastrointestinal symptom‐specific anxiety. We therefore divided these data into equally sized tertiles across the entire cohort of participants. We used the 10‐item version of the Cohen perceived stress scale (CPSS) to assess perceived stress. This is derived from the original 14‐item instrument, ²⁵ and is psychometrically reliable and comparable with it. ²⁶ It measures experience of stress in the previous month. Again, with no validated cut offs to define levels of perceived stress, we divided data into tertiles across the entire cohort.