BillMonk Spreads Like a Happy Virus

One of the reasons BillMonk has been growing so well is that friends add friends who add more friends. You have an incentive to add your friends because it makes your lives easier. Being the geeks we are, we wanted to visualize this.

This is just a small part of the BillMonk universe. Each dot is a person; bigger dots mean more recent user activity (the very first two users, Gaurav and Chuck, are the colored dots). Lines with arrows (which you can’t see very well) represent a new user invitiation, and lines without arrows show friendships.

Here are some observations:

• There are some long chains of person to person to person, which is just neat
• There are lots of clusters, which correspond to real-world groups of friends
• These clusters usually start with one person (the seed), but often other friends pass it on within the same group or even spread it to a new circle of friends (it’s easy to see the people who span multiple groups)
• There tend to be two different group patterns:
• One primary billkeeper is entering bills on behalf of the group (we’d guess these are probably roommate situations)
• Everyone is creating transactions with everyone else
• Lots of people are using BillMonk regularly
• One thing this graph doesn’t show you is that people often check out the site, then come back a week later when they have a need for BillMonk

Whenever we do this kind of analysis, we are always very careful to protect user privacy. The first thing we do is to strip all potentially identifying information. (The exception in this case is for ourselves as users).