Development of a digestive health status instrument: Tests of scaling assumptions, structure and reliability in a primary care population

Background: The absence of valid and reliable health status measures for functional gastrointestinal illness has limited research and patient care for this common group of disorders. A self-report survey has been developed. Methods: Initial development focused on extensive pretesting of patients, primary care physicians and gastroenterologists. The disease-specific portion included the Rome criteria for dyspepsia subgroups and the Manning and Rome criteria for irritable bowel syndrome. The Short Form-36 was added. Psychometric analyses included techniques of multitrait scaling, scale internal consistency and criterion validation. Results: Six hundred and ninety patients presenting to their primary care physician for treatment of heartburn, abdominal pain or discomfort completed the 98 question survey. The disease-specific portion revealed five components including reflux, dysmotility, a two-domain bowel dysfunction complex, and a pain index. Internal consistency measures demonstrated good to excellent reliability. Scaling successes were observed on multitrait scaling. The disease-specific portion was reduced to 34 questions. Criterion validity was demonstrated with the correlation of the disease-specific questions to the SF-36. Conclusions: The psychometric analyses lend credence to the concept of stomach and bowel symptom subgrouping as proposed by expert consensus. The psychometric properties of the five summated disease-specific scales compare favourably with standardized health status measures.