As Twitter continues to grow, it appears that something else is also expanding: the gap between the most popular users and everyone else.

The latest study from Rapleaf investigated this “popularity gap,” finding some interesting discrepancies just between groups of users in the top 0.1%, 1%, and 10% of Twitter popularity. Completely contrary to Facebook, where having more friends doesn’t necessarily mean you’ll have any more friend invitations rolling in than other users, the most followed users on Twitter gain followers at a much faster rate than do less popular tweeters.

According to their research comparing average number of followers in March and in June, Rapleaf discovered a marked difference in percentages of added followers. For the top 0.1% of users, average number of followers nearly quadrupled, whereas for the top 1% and 10% groups, average number more than doubled.

That’s a considerable drop-off, and it’s possible that the numbers continue to drop exponentially, meaning less popular users add followers at slower and slower rates.

Another major conclusion of the study finds that users in the top 0.1% have about five times as many followers as those in the top 1% and around 40 times as many as those in the top 10%. This makes a lot of sense considering the rates of follower growth described above.

While some might see these numbers as a mere reflection of Twitter’s surge in popularity earlier this year, there might be something here that reveals what kind of social networking site Twitter really is.

Again, Facebook users probably wouldn't return similar results to these because having more friends shouldn’t mean you’re going to be accepting new invitations all the time. In fact, if you’re already connected to most of your friends, it should demonstrate opposite results. It would be interesting to see this particular study applied to Facebook fan pages, which—with celebrity and company profiles welcome—may mirror Twitter’s functionality better.