Entry requirements and membership homogeneity in online patient groups.

The objective was to explore a relationship between the economics of religion and the attributes of online patient groups by testing the hypotheses that (1) the harsher the entry requirements to an online patient group, the more active its members are; and (2) membership homogeneity in a given group is reflected in the educational level of group members. Online groups were randomly chosen from the 'Yahoo groups' category of 'Illnesses'. The hypothesis about entry requirements was narrowed by defining those requirements as either 'Open', 'Register', or 'Closed'. The number of messages over a 4-month period in each of 162 different groups was tallied. The hypothesis about membership homogeneity was refined by counting the citations in messages and by predicting the educational level of members (as reflected in the average word length of messages) based on these citation counts. Across 162 groups, the number of messages was significantly less in Open groups than in Register groups and less in Register groups than in Closed groups. Across 14 groups, the average word length of messages in a group positively correlated with the number of citations in that group. The hypothesis is supported that increased group entry barriers correspond to increased group message activity and members tend to be similar within a group. These attributes could be used to help design effective groups.