Conversations can be measured by the number of contributors in each thread (depth of the thread). The absolute number of contributors is not necessarily a reliable measure since it can give you a distorted picture of reality. For example, a thread with 10 comments contributed by 2 people is less valuable than a thread with 10 comments contributed by 4 people. The conversation composed of 4 unique contributors gives a better indication of the sense of community.
When doing our analysis we accounted for the number of unique contributors for a set of communities across our database. The average across the communities is 3.79 unique contributors per topic (including the topic starter). The unique contributors per topic are being calculated on an all time basis, where we calculate the average of unique contributors per community. To strive for an ideal sense of community is it advised to focus on an average amount of unique contributors per topic of 3.5 and above.