Health virtual communities are a major channel through which health consumers share health-related knowledge and/or exchange social support with their peers. Because of the collaborative nature of health virtual communities, user participation is a critical factor for community growth and prosperity. In this study, we examine the impact of reciprocity on user participation within health virtual communities. Additionally, we investigate the impact of the homophily (similarity of user characteristics such as age, gender, and tenure) on user participation. To do so, we analyzed 1947 messages exchanged between 130 users and their peers. Our results support short-term reciprocity, but refute the positive relationship associated with long-term reciprocity. Among homophily hypotheses, our results support gender homophily, but not age homophily and tenure homophily
