Balshaw, R, et al. “LONGITUDINAL OUTCOMES OF GASTROINTESTINAL SYMPTOMS IN CANADA (LOGIC): KEY FACTORS FOR AN EFFECTIVE PATIENT RETENTION IN OBSERVATIONAL STUDIES”. Journal of Population Therapeutics and Clinical Pharmacology, vol. 16, no. 1, Dec. 2018, https://mail.jptcp.com/index.php/jptcp/article/view/271.