A Valid and Reliable Measure of Constipation-Related Quality of Life

Abstract

Few existing measures assess constipation-specific quality of life. This study sought to develop a valid and reliable quality-of-life measure for constipation. First, we created a preliminary instrument that assessed quality-of-life domains affected by constipation: body image, eating, mood, and relationships with others. We conducted focus groups both with patients with constipation seeking treatment and the health care providers who treat them. Next, a 59-item questionnaire was given to 240 subjects with constipation (83% female) and 103 healthy volunteers (63% female). Test-retest reliability and discriminant, convergent, and divergent validity were assessed. Exploratory factor analysis revealed four domains: Social Impairment (five items), Distress (six items), Eating Habits (three items), and Bathroom Attitudes (four items). Internal consistency and test-retest reliability for all subscales was high (Cronbach's alpha = 0.89; intraclass correlation coefficient = 0.87). All domains discriminated well between subjects with constipation and healthy volunteers (P < 0.001). Convergent validity was excellent: all subscales correlated highly with the Irritable Bowel Syndrome Quality of Life Scale total score (P < 0.001) and the Medical Outcomes Study Short Form-36 physical component and mental component summary scores (P < 0.001). Scores from our Constipation-Related Quality of Life measure were not significantly correlated with the Social Desirability Scale, demonstrating divergent validity. Our findings support the reliability and validity of the Constipation-Related Quality of Life measure. Future validation of the Constipation-Related Quality of Life measure for assessing changes in quality of life in response to treatments for constipation is needed.