Characteristics of non-responders to self-reported questionnaires in a large inflammatory bowel disease cohort study

Abstract

Background. A major threat to the validity of longitudinal cohort studies is non-response to follow-up, which can lead to erroneous conclusions. The objective of this study was to evaluate the profile of non-responders to self-reported questionnaires in the Swiss inflammatory bowel disease (IBD) Cohort. Methods. We used data from adult patients enrolled between November 2006 and June 2011. Responders versus non-responders were compared according to socio-demographic, clinical and psychosocial characteristics. Odds ratio for non-response to initial patient questionnaire (IPQ) compared to 1-year follow-up questionnaire (FPQ) were calculated. Results. A total of 1943 patients received IPQ, in which 331 (17%) did not respond. Factors inversely associated with non-response to IPQ were age >50 and female gender (OR = 0.37; p < 0.001 respectively OR = 0.63; p = 0.003) among Crohn’s disease (CD) patients, and disease duration >16 years (OR = 0.48; p = 0.025) among patients with ulcerative colitis (UC). FPQ was sent to 1586 patients who had completed the IPQ; 263 (17%) did not respond. Risk factors of non-response to FPQ were mild depression (OR = 2.17; p = 0.003) for CD, and mild anxiety (OR = 1.83; p = 0.024) for UC. Factors inversely associated with non-response to FPQ were: age >30 years, colonic only disease location, higher education and higher IBD-related quality of life for CD, and age >50 years or having a positive social support for UC. Conclusions. Characteristics of non-responders differed between UC and CD. The risk of non-response to repetitive solicitations (longitudinal versus transversal study) seemed to decrease with age. Assessing non-respondents’ characteristics is important to document potential bias in longitudinal studies.

Key Words:

• cohort study
• Crohn’s disease
• inflammatory bowel disease
• selection bias
• self-administrated questionnaires
• ulcerative colitis

Acknowledgements

This study was carried out by all the gastroenterologists and investigators listed in the Appendix. We thank Carla Vaucher for proofreading the manuscript. The study is supported by the Swiss National Science Foundation grants N°33CS30-148422 (Swiss IBD cohort study), and 32473B-138498 (Appropriateness of care in IBD).

Statement of authorship: Study design and conception (VP, JPV), statistical analysis (EM, NF), analysis and interpretation (VP, EM, CM, JPV, BB, PM), drafting the article or revising it critically for important intellectual content (VP, EM, CM, AS, NF, BB, PM, JPV), final reading and approval of the manuscript (VP, EM, CM, AS, NF, BB, PM, JPV).

Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.