Background Internet-based participation has the potential to enhance pragmatic and decentralized trials, where representative study populations and generalizability to clinical practice are key. We aimed to study the differences between internet and noninternet/telephone participants in a large remote, pragmatic trial.Methods and Results In a subanalysis of the ADAPTABLE (Aspirin Dosing: A Patient-Centric Trial Assessing Benefits and Long-Term Effectiveness) study, we compared internet participants with those who opted for noninternet participation. Study process measures examined included participant characteristics at consent, study medication adherence, and study retention. The clinical outcome examined was a composite of all-cause mortality, hospitalization for myocardial infarction, or hospitalization for stroke. Noninternet participants were older (mean 69.4 versus 67.4 years), more likely to be female (38.9% versus 30.2%), more likely to be Black (27.3% versus 6.0%) or Hispanic (11.1% versus 2.0%), and had a higher number of comorbid conditions. The composite clinical outcome was more than twice as high in noninternet participants. The hazard of nonadherence to the assigned aspirin dosage was 46% higher in noninternet participants than internet participants.Conclusions Noninternet participants differed from internet participants in notable demographic characteristics while having poorer baseline health. Over the course of ADAPTABLE, they also had worse clinical outcomes and greater likelihood of study drug nonadherence. These results suggest that trials focused on internet participation select for younger, healthier participants with a higher proportion of traditionally overrepresented patients. Allowing noninternet participation enhances diversity; however, additional steps may be needed to promote study retention and study medication adherence.
