Cohort studies follow groups of people to understand disease. They are difficult to organize and often do not focus on patient-reported outcomes. Internet-based cohort studies provide new opportunities to study patient-reported outcomes; they are also efficient and can easily include large numbers of people. Linking an Internet-based cohort study, like CCFA-Partners, to a traditional cohort study can be beneficial to both studies and add a tremendous amount of information about a disease. Therefore, we aimed to link CCFA-Partners with the Ocean State Crohn's and Colitis Area Registry (OSCCAR) and The Sinai-Helmsley Alliance for Research Excellence (SHARE), both of which are traditional cohort studies. OSCCAR is a cohort of patients with inflammatory bowel disease (IBD) in Rhode Island. SHARE is a cohort across 7 academic medical centers around the United States. Both cohorts collect specimens, like blood and stool, from participants. OSCCAR enrolled people with IBD from 2008 to 2013. SHARE started enrolling people with IBD in July 2012 and enrollment is continuing. People in the cohorts who had access to the Internet were told about CCFA-Partners by the study coordinators and encouraged to enroll.

In the OSCCAR cohort, 243 of the 320 participants consented to join the CCFA-Partners cohort. However, only 44 participants completed enrollment in CCFA-Partners. OSCCAR participants who completed enrollment were better educated than those who did not complete enrollment. In the SHARE cohort, 436 participants completed enrolment in CCFA-Partners. SHARE participants who completed enrollment were more often women and white. If they had Crohn's disease, those who completed enrollment had fewer disease symptoms and if they had ulcerative colitis, those who completed enrollment had less extensive disease. Linkage of CCFA Partners with cohorts such as OSCCAR and SHARE may be a cost-effective way to expand opportunities for research. Although linkage is possible, participant's willingness to complete the linkage is the limiting factor. Asking participants in a traditional cohort at the time of enrollment may be a way of maximizing linkage to CCFA-Partners.