Those are the three measures being pointed out by this research paper. In my case, (2) and (3) are the same. My first name is my Twitter name. When you retweet me, when you reply to me, you mention my name.
Just when I am getting in a mood to increase my interaction levels on the Twitter platform, this research paper came my way. I am surprised they did not list a fourth metric: (4) How many times have you been listed? A subset of that item might be: (5) How many people are following those lists?