<p>I read a research paper about that. You can find it at <a href="http://arxiv.org/abs/1105.5170" rel="nofollow">http://arxiv.org/abs/1105.5170</a></p>

<p>The researchers where interested in studying the "strong relationships" in the twitter social graph and they are using metrics base on the number of message between the user (@... mentions).</p>

<p>I'm not a twitter user, but this looks like what you want to do. They add access to the whole social network, which is not available to everyone, but it could probably be adapted for a single user.</p>
Finding Top Twitter Friends Using Python
<p>What's the best way to find someone's top friends on twitter? </p>

<p>I'm trying to figure out a way to see who they interact with the most, but I am not sure what the best way is of doing this. Also, there are obvious things to check (is the username following that person, etc etc). </p>

<p>I imagine someone else has thought about this, so I am trying to get a little smarter on it. I am using Python to figure this out. Any help would be great.</p>