  Online health communities provide a knowledge exchange platform for a wide
range of diseases and health conditions. Informational and emotional support
helps forum participants orient around health issues beyond in-person doctor
visits. So far, little is known about the relation between the level of
participation and participants' contributions in online health communities. To
gain insights on the issue, we analyzed 456 posts in 56 threads from the
Dermatology sub-forum of an online health community. While low participation
threads (short threads) revolved around solving an individual's health issue
through diagnosis suggestions and medical advice, participants in high
participation threads (long threads) built collective knowledge and a sense of
community, typically discussing chronic and rare conditions that medical
professionals were unfamiliar with or could not treat effectively. Our results
suggest that in short threads an individual's health issue is addressed, while
in long threads, sub-communities about specific rare and chronic diseases
emerge. This has implications for the user interface design of health forums,
which could be developed to better support community building elements, even in
short threads.
